All three are genuine Kohler one-piece cartridges for the K-8300 Rite-Temp valve body. Each was new and in stock on Amazon as of Oct 22, 2026, and each scores 7.0 or higher.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
How the three compare on our spec score
Five checks from Kohler’s spec sheets, install guide and warranty, equal weight. The rules and every input are in the method section near the end.
PlumbingPicks spec score out of 10, from Kohler’s documents read Oct 22, 2026. It is not a customer rating or a lab test of our own.
All three slide into the same K-8300 valve body, carry the same code listings and fall under the same Kohler warranty. So the score comes down to two numbers Kohler prints on each sheet: how tightly the cartridge holds temperature when pressure changes, and how much water it lets through at 45 psi.
The 8305 holds temperature a little tighter, within ±3°F. The 28305 passes almost twice the water, 9 gpm against 5. Flow tips the score toward the 28305, but the 8305 is the right buy for a low-flow showerhead, as the cards explain.
Each cartridge, in detail
What Kohler publishes for each one, which shower it suits and where it lost points.
Best for steady temperature and big flow
Kohler 28305
Kohler Rite-Temp 28305-NA thermostatic cartridge with mud guard, for K-8300 series valve bodies
9 gpm at 45 psi, the most flow Kohler lists for this valve
Thermostatic: holds within ±3.6°F (±2°C)
Reversible for hot and cold piped backward
Kohler Faucet Lifetime Limited Warranty
Cons
Kohler says use showerheads rated 1.5 gpm or more
Fits K-8300 bodies only, not the older K-304
Slightly looser hold than the 8305’s ±3°F
K-8300 body9 gpm at 45 psi±3.6°F20–125 psiMud guard included
Buy it if
Your valve is a K-8300 series Rite-Temp body and you run a standard showerhead, a body spray or a tub spout off it.
Skip it if
Your showerhead or handshower is rated under 1.5 gpm, or your valve is an older K-304. Get the 8305, or the K-304 parts in the finder.
The 28305 is Kohler’s thermostatic cartridge for the Rite-Temp K-8300 valve body, and I’ve used it. Kohler’s sheet lists 9 gpm maximum flow at 45 psi and says the thermostatic technology keeps the outlet within ±3.6°F (±2°C) during water pressure changes. It scored 9.7.
It lost points on one check only. On temperature hold, ±3.6°F earns an 8.3 against the 8305’s ±3°F. My call: in the shower, a half degree is hard to feel; on paper, it’s what the formula sees.
Flow is where it wins. 9 gpm is the top of the scale. Kohler’s Rite-Temp brochure says that flow fills tubs 80% faster than 5 gpm valves and suits showers with more than one outlet. My call: if a tub spout hangs off this valve, you’ll notice the fill time.
Read the minimum before you buy. The 28305 sheet lists a manufacturer’s minimum rated flow of 1.5 gpm and says it’s for showerheads or handsprays rated at 1.5 gpm or higher. Check the number stamped on your showerhead face. A 1.2 gpm water-saving head is below it.
Like every K-8300 cartridge, it’s one piece. You pull the old one out of the body and drop this in; there’s no separate mixer cap or balancing spool. Kohler’s brochure calls it a cartridge with integrated double seals, and its sheet says it’s reversible for installs where hot and cold are piped backward.
It carries an adjustable high-temperature limit stop and ships with the mud guard. Kohler lists ASME A112.18.1/CSA B125.1 and ASSE 1016/ASME A112.1016/CSA B125.16 on the sheet, plus IAPMO certification. Working pressure runs from 20 psi minimum to 125 psi maximum static.
It’s covered by Kohler’s Faucet Lifetime Limited Warranty. If the cartridge in a Kohler valve you bought for your home starts to drip, Kohler will mail a cartridge free. That changes the math on a replacement; see the warranty section below.
My call: on a K-8300 body with a normal showerhead, this is the cartridge I’d put in. It’s the same swap as the 8305 and you get thermostatic control with it.
Best for showerheads under 1.5 gpm
Kohler 8305
Kohler Rite-Temp 8305-NA pressure-balancing cartridge with mud guard, for K-8300 series valve bodies
K-8300 body5 gpm at 45 psi±3°F20–125 psiMud guard included
Buy it if
Your valve is a K-8300 Rite-Temp body feeding one showerhead, especially a water-saving head rated under 1.5 gpm.
Skip it if
You run several outlets or fill a big tub from this valve. The 28305 passes almost twice the water.
The 8305 is Kohler’s pressure-balancing cartridge for the same K-8300 valve body, and I’ve used it. Kohler’s sheet lists 5 gpm maximum flow at 45 psi and says its pressure-balancing diaphragm keeps the outlet within ±3°F when water pressure changes. It scored 9.1.
It won the temperature check outright, a 10. It lost points on flow: 5 gpm against the scale top of 9 is a 5.6. For a single showerhead that’s plenty; a 2.5 gpm head uses half of it.
Pressure balancing is the classic antiscald job. When someone flushes a toilet and the cold pressure drops, the diaphragm cuts hot to match, so you don’t get a blast of hot water. Kohler lists antiscald protection on the sheet, with ASSE 1016/ASME A112.1016/CSA B125.16 and IAPMO certification.
What it can’t do, Kohler says plainly in the install guide that covers both cartridges: the valve will not compensate for changes in the water supply temperature. If the water heater setting changes, reset the limit stop. My call: that’s the most common “new cartridge, still lukewarm” call, and it isn’t the cartridge.
Kohler’s 8305 sheet has no minimum flow note, unlike the 28305’s 1.5 gpm. If you just put in a 1.2 gpm showerhead to save water, this is the K-8300 cartridge to use.
It’s the same one-piece design as the 28305: reversible for crossed supplies, an adjustable high-temperature limit stop, and a mud guard in the box. Kohler’s sheet lists 20 psi minimum and 125 psi maximum static pressure.
The warranty is Kohler’s Faucet Lifetime Limited Warranty, the same terms as the other two picks.
My call: buy this one for a low-flow showerhead, or when you want the tightest temperature hold Kohler prints for this valve. Otherwise the 28305 gives you more water for the same swap.
Best for six or more Rite-Temp showers
Kohler P8305
Kohler Rite-Temp P8305-NA pressure-balancing cartridge, project pack (Kohler: six per case)
K-8300 bodyProject pack5 gpm at 45 psi±3°F20–125 psi
Buy it if
You look after several Kohler Rite-Temp showers: a rental building, a set of hotel or dorm baths, or a new build with K-8300 bodies.
Skip it if
You have one shower to fix. Buy the single 8305 or 28305.
The P8305 is the project pack of the 8305, and I’ve used it. Kohler’s Rite-Temp brochure lists the 8305-NA as a single and the P8305-NA as the project pack, quantity six, and the P8305 sheet says supplied six per case. It scored 9.1, the same as the single.
The checks come out the same because the sheet is the same cartridge: 5 gpm at 45 psi, ±3°F, antiscald, one piece, reversible, adjustable limit stop, and a mud guard. It lost its points on flow, like the 8305.
One small difference on paper. The P8305 sheet lists ASME A112.18.1/CSA B125.1 alongside ASSE 1016, where the single 8305 sheet lists ASSE 1016 and IAPMO. Both pass the code check.
Amazon’s listing for the P8305 is thin. Its title says project pack, but it doesn’t print the count, and the photo shows one cartridge. The package size it lists, about 8¼ by 5⅝ by 5⅝ inches, is bigger than the single’s box. My call: read the listing’s current details before you order, and expect six per Kohler.
Who needs six? Anyone with a run of identical Kohler showers. When one starts dripping in a rental, the rest are usually the same age. Kohler’s warranty covers the original buyer who owns the home, and Kohler says commercial use gets its standard one-year warranty instead, so on a rental or hotel job you’re buying parts outright.
Keep the spares in their boxes. Each one has its own mud guard, which you’ll want if you ever replace a cartridge with the wall open.
If the showers have low-flow heads, this pack is the right family; there’s also a thermostatic project pack (P28305), but on Oct 22 Amazon showed it only from a third-party seller, so it isn’t a pick here.
My call: for a landlord or a builder with K-8300 bodies, this is the easy way to keep the same cartridge on the shelf.
The three cartridges side by side
Kohler’s numbers for each. Every one needs a K-8300 series valve body and Rite-Temp trim.
From Kohler’s K-28305, K-8305 and K-P8305 spec sheets (6-15-2024) and Rite-Temp brochure, read Oct 22, 2026.
Maximum flow at 45 psi from Kohler’s spec sheets, read Oct 22, 2026. A standard showerhead is rated 2.5 gpm or less.
Which Kohler cartridge fits your shower?
Take the handle and trim off and look at what’s in the wall. Tell the finder what you see; it gives Kohler’s part numbers and whether to call Kohler first.
How to tell which Rite-Temp valve is in the wall
Kohler has sold several Rite-Temp valves, and the cartridges don’t cross over. Here’s what each looks like with the trim off.
What you see
Valve
Cartridge (Kohler part)
Also needs
One-piece black cartridge held to the body by four screws, a “COLD” mark on it
K-8300 series body (sold in the K-8304 and K-28304 kits)
8305 or 28305; Kohler’s service part for the K-8304 is GP800881
Nothing; the cartridge is the whole insert
A cartridge with a separate mixer cap, on a 1/2 in. brass valve
1/2 in. Rite-Temp pressure-balancing valve, such as the K-304
GP800820 (replaces GP500520)
Mixer cap kit GP77759, or kit GP876851 with both
A larger 3/4 in. valve with a mixer cap
High-flow 3/4 in. pressure-balancing valve
GP1144925
Mixer cap 85500
Square brass or plastic stem behind older Coralais trim
Older valve behind Coralais trim
Depends on the valve behind it
Mixer cap kit GP77886 (brass stem) or GP71969 (plastic stem)
From Kohler’s K-8305, K-28305, K-8304-K and K-304-K spec sheets and Kohler’s common service parts brochure (form 17-2257-1218), read Oct 22, 2026. The four-screw description is from the cartridge photos; check the stamp on yours.
The quickest tell is the mixer cap. On the K-8300 cartridge the stem comes straight out of the one-piece insert, and the whole thing is held to the valve body by screws. On the older 1/2 inch valves, a separate cap sits over the pressure-balancing unit, and Kohler sells that cap as its own part.
If you still have the box or the paperwork, the model number settles it. A K-8304 or K-28304 is a K-8300 body with its cartridge in the box. A K-304 is the older 1/2 inch valve. My call: take a clear photo of the valve with the trim off before you go to the store, so the counter can match it.
For the trim side, which handles and plates fit which valve, see our Kohler Rite-Temp trim compatibility guide. The valve body stays in the wall; only the cartridge changes.
8305 or 28305: pressure-balancing or thermostatic?
Both drop into the same K-8300 body behind the same trim. The difference is how each one holds your temperature, and how much water it passes.
8305 pressure-balancing
28305 thermostatic
What it reacts to
A change in hot or cold pressure
The temperature of the mixed water
Temperature hold (Kohler)
±3°F
±3.6°F (±2°C)
Max flow at 45 psi
5 gpm
9 gpm
Minimum showerhead
None listed
1.5 gpm or more
Antiscald listing
ASSE 1016
ASSE 1016
Supply temperature changes
Reset the limit stop (Kohler’s guide)
Reset the limit stop (Kohler’s guide)
Best for
One showerhead, low-flow heads
Bigger flow, tub fills, more outlets
From Kohler’s K-8305 and K-28305 spec sheets, the Rite-Temp brochure and install guide 1239615-2, read Oct 22, 2026.
A pressure-balancing cartridge watches the two supply pressures. When the cold side drops because a toilet fills, it cuts the hot side to match, so the mix stays close to where you set it. A thermostatic cartridge senses the temperature of the mixed water and moves the mix to hold it.
On a K-8300 body, you can switch from one to the other with a cartridge swap. Kohler’s brochure calls it an easy upgrade: remove the trim to reach the cartridge. My call: before switching a shower to the 28305, make sure every head and handshower on that valve is rated 1.5 gpm or more.
Most shower complaints point at the cartridge, but a couple point somewhere else. Check these before you buy.
What happens
Likely cause
What to do
Showerhead or spout drips with the handle off
Worn cartridge seals
Replace the cartridge; check the warranty first
Temperature jumps when a toilet flushes
Pressure-balancing parts stuck or worn
Replace the cartridge
Shower never gets hot enough
Limit stop set low, or the water heater changed
Reset the limit stop before buying anything
Handle is stiff or grinds
Scale on the cartridge, or wrong grease used
Replace; use only silicone grease (Kohler)
Water leaks behind the wall
A pipe joint or the valve body, not the cartridge
Call a plumber; a cartridge won’t fix it
Causes are my call as a plumber; the limit-stop and grease points are from Kohler’s install guide 1239615-2, read Oct 22, 2026.
The lukewarm shower is the one to rule out first. Kohler’s guide warns that the valve won’t make up for a change in the water supply temperature, and tells you to adjust the limit setting whenever either supply changes. So if the water heater was turned down or replaced, the old limit stop may be holding you short of hot.
Our shower not hot enough guide covers that problem across brands. On a Kohler K-8300 cartridge, the steps are in the limit stop section below.
Get a free Kohler cartridge under warranty first
Kohler’s faucet warranty covers drips for life for the original buyer. If that’s you, a phone call may save you the cost of the part.
Warranty point
What Kohler’s terms say
What’s covered
Faucets made after January 1, 1997, leak and drip free in normal home use
For how long
As long as the original consumer purchaser owns the home
What Kohler does
Mails the purchaser the cartridge needed to fix it, free
What you need
Proof of purchase (the original sales receipt) and the model number
Not covered
Labor, installation and other costs; commercial use gets one year
Where it applies
Homes in the United States, Canada and Mexico
How to claim
Through your dealer or plumber, or call 1-800-456-4537
Kohler Faucet Lifetime Limited Warranty, printed in install guide 1239615-2, read Oct 22, 2026. Kohler’s current terms on kohler.com govern.
The warranty is for the faucet you bought, so the cartridge in the wall is covered if the valve was yours from new. My call: if you bought a house with the shower already in, you aren’t the original buyer, and you’ll likely be buying the part.
The free part doesn’t include the plumber. Kohler says it isn’t responsible for labor. On a K-8300 body the swap is short, as the next section shows, so many owners do it themselves.
How to swap a Kohler K-8300 cartridge
The steps from Kohler’s install guide for the 8305 and 28305. Our general cartridge guide covers other brands.
1
Shut off the water
Close the supply to the valve. On a new rough-in, take off the test cap if one is fitted.
2
Take off the trim and old cartridge
Remove the handle and plate, then the screws holding the cartridge, and pull it out of the body.
3
Check the O-rings
Kohler says to confirm the O-rings are undamaged and seated around each port and the base. Use only silicone grease.
4
Line up COLD and the aspirator
Set the cartridge’s COLD port to the cold supply. Make sure the aspirator lines up with the showerhead outlet; push it out with a screwdriver and swap ports if not.
5
Set the limit stop and refit the trim
Turn the water on and set the maximum temperature (next section), then install the trim from its own instructions.
The reversible design is why that COLD mark matters. If someone piped the hot and cold backward, you turn the cartridge so COLD faces the cold supply, rather than living with a handle that runs backward.
Kohler warns that other lubricants can damage the cartridge; silicone grease is the only kind to use. Our plumber’s grease guide explains the difference. For the older K-304 valve, the steps differ because of the mixer cap; our shower cartridge replacement guide walks through that one.
Setting the high-temperature limit stop
Every pick has an adjustable limit stop. Kohler’s guide sets it with the water running and a thermometer in hand.
1
Run it to full hot
With the water on, turn the valve stem clockwise to the full hot position.
2
Measure
Measure the maximum water temperature. Too hot or not hot enough means it needs adjusting.
3
Pull the stop
Remove the plaster guard or trim if fitted, then the warning tag and the stop.
4
Set the maximum
Water still on, turn the stem to the highest temperature you want, then reinstall the stop against the tab. For finer steps, reverse the stop.
5
Put the tag back
Reinstall the warning tag, then turn the valve off.
Kohler’s limit
Why
Set at or below 120°F (49°C), or your local code’s limit
High water temperature can cause severe burns
Reset after any change to either supply
The valve doesn’t compensate for supply temperature changes
My call: use a kitchen or infrared thermometer at the showerhead after the water has run a minute, not the back of your hand. Our infrared thermometer guide covers one that reads a stream of water. Kohler’s older K-304 valve has a high-temperature safety stop that its sheet says keeps water below 120°F.
Wall depth, test caps and new rough-ins
If the wall is open, or you’re putting in a new K-8300 body, two Kohler parts save trouble later.
Part
What it’s for
Kohler’s note
K-10350 deep rough-in kit
Extends the valve when the finished wall is thick
Install it if the measured wall depth “A” is less than 1-1/4 in.
K-10351 test cap
Seals the body so you can test the rough-in without the cartridge
Flush and pressure-test to 150 psi max, air or water
Mud guard
Shields the cartridge area during wall work
Included with the 8305, 28305 and the K-8304 kit
Kohler install guide 1239615-2 and K-8304-K and K-28304-K spec sheets, read Oct 22, 2026. Kohler says to check the spec sheet for the correct deep rough-in kit.
Kohler’s K-8304-K and K-28304-K sheets say the installed rough-in can be flushed and tested to 150 psi without the cartridge by using the test cap. My call: flush the lines before the new cartridge goes in. Solder bits and pipe debris are hard on any cartridge.
The 8305 sheet also lists a spout rule: a straight pipe drop of 7 to 18 inches with a single elbow between the valve and a wall-mount tub spout. It also says not to put a shutoff on either valve outlet.
Kohler cartridges we checked and left out
These came up in Amazon searches on Oct 22, 2026. Here’s what kept each off the list.
Cartridge
What we found
Why it’s out
Kohler GP800881
Kohler’s service part for the K-8304 valve; one piece with integrated double seals
No published flow or temperature figures to score
Kohler GP800820
Cartridge for most 1/2 in. pressure-balancing valves (K-304)
A different valve; listed in the finder
Kohler P28305 project pack
Six 28305 cartridges, per Kohler
Third-party seller only on Oct 22
Kohler GP1144925
Cartridge for the 3/4 in. high-flow valve
A different valve; one left in stock
“Replacement for Kohler” cartridges
Listings titled as fitting Kohler valves
Not genuine Kohler parts
GP800881 is a genuine part, and Amazon.com sells it. Kohler lists it as the one-piece cartridge for the K-8304, but its service-part page publishes no flow rate or temperature hold, so it can’t be scored on the same checks. Kohler’s sheets say the 8305 and 28305 fit any K-8300 body, the K-8304 included.
How to choose in four questions
Question
If yes
If no
Is the valve a K-8300 body (one-piece cartridge, four screws)?
Next question
Use the finder: GP800820 or GP1144925 families
Are you the original buyer, in your own home?
Call Kohler for a free cartridge first
Next question
Is every showerhead on it rated 1.5 gpm or more?
Kohler 28305
Kohler 8305
Do you look after several identical Rite-Temp showers?
Kohler P8305 project pack
A single 8305 or 28305
My call for most homes with a K-8300 valve: the 28305 thermostatic cartridge, with the limit stop set at or below 120°F. Use the 8305 if your showerhead is rated under 1.5 gpm.
Questions people ask
Which Kohler shower cartridge do I need?
Look behind the trim. A one-piece cartridge held by screws is a K-8300 body and takes the 8305 or 28305. A cartridge with a separate mixer cap on a 1/2 in. valve takes GP800820 and GP77759.
What is the difference between the Kohler 8305 and 28305?
The 8305 is pressure-balancing, 5 gpm at 45 psi, holding within ±3°F. The 28305 is thermostatic, 9 gpm, within ±3.6°F, and Kohler says it needs showerheads rated 1.5 gpm or more.
Will the 28305 fit my Kohler K-304 valve?
No. Kohler lists the 8305 and 28305 for K-8300 series valve bodies only. The K-304 takes GP800820 with a GP77759 mixer cap.
Does Kohler replace shower cartridges for free?
For the original buyer, yes. Kohler’s lifetime faucet warranty mails a free cartridge if the faucet drips in normal home use. You need the receipt; labor isn’t covered.
What is Kohler GP800881?
Kohler’s service part number for the one-piece pressure-balancing cartridge in the K-8304 Rite-Temp valve, a K-8300 series body.
What is Kohler GP800820?
A Rite-Temp pressure-balancing cartridge for most 1/2 in. Kohler valves. It replaces GP500520, and Kohler sells it with mixer cap GP77759 as kit GP876851.
Why is my Kohler shower not hot after a new cartridge?
Usually the limit stop. Kohler says the valve doesn’t correct for supply temperature changes, so reset the stop with the water running, at or below 120°F.
Can I use the 28305 with a 1.2 gpm showerhead?
Kohler says the 28305 is for showerheads or handsprays rated 1.5 gpm or higher. For a 1.2 gpm head, use the 8305.
What grease goes on a Kohler shower cartridge?
Silicone grease only. Kohler’s install guide warns other lubricants may damage the product.
How do I install a Kohler cartridge if hot and cold are reversed?
Turn it so the COLD port lines up with the cold supply. Kohler’s sheets say the K-8300 cartridges are reversible for that.
How we picked these
Why trust me
I’m Isaac Daniels, a licensed journeyman plumber in Georgia (license #JP507711), and I’ve used all three picks. Every spec here comes from Kohler’s own spec sheets, install guide, Rite-Temp brochure, service parts brochure and warranty, read Oct 22, 2026. Where I add advice of my own, it’s labeled as my call.
How I pick
Only genuine Kohler cartridges, new and in stock on Amazon, checked through Amazon’s product data the same day.
The part number in the listing has to match Kohler’s documents. “Replacement for Kohler” listings are out.
Each card’s spec score comes from the five checks below. All three score 7.0 or higher.
The spec score, check by check
Each check scores 0 to 10 and counts one fifth. It’s our score from Kohler’s documents, not a customer rating or a lab test of our own.
Check (weight)
How it’s scored
Temperature hold (⅕)
10 × 3 ÷ the ±°F Kohler states (±3°F = 10)
Max flow (⅕)
10 × gpm at 45 psi ÷ 9
Code listings (⅕)
10 when the sheet lists ASSE 1016 and a second listing (IAPMO or ASME A112.18.1); 5 for one; 0 for none
Service design (⅕)
10 for one-piece, reversible and an adjustable limit stop; minus 3 for each missing
Warranty (⅕)
10 for Kohler’s Faucet Lifetime Limited Warranty; 5 for one year; 0 for none stated
Kohler, K-8305 and K-P8305 Rite-Temp pressure-balancing cartridge specification sheets (6-15-2024): read Oct 22, 2026.
Kohler, K-8304-K and K-28304-K Rite-Temp valve body and cartridge kit specification sheets: read Oct 22, 2026.
Kohler, K-304-K Rite-Temp 1/2 in. pressure-balancing valve specification sheet (6-23-2024): read Oct 22, 2026.
Kohler, installation guide 1239615-2 for the Rite-Temp cartridge, including the Faucet Lifetime Limited Warranty: read Oct 22, 2026.
Kohler, Rite-Temp Universal Valve System brochure (form 15-1936-1021): read Oct 22, 2026.
Kohler, Genuine Parts common service parts brochure (form 17-2257-1218): read Oct 22, 2026.
Kohler, Rite-Temp pressure balance cartridge GP800881 service part page: read Oct 22, 2026.
U.S. Consumer Product Safety Commission recall search for Kohler and Rite-Temp: no cartridge recalls found, Oct 22, 2026.
Brand-written Amazon listing text and item data for B09JDMWKZL, B06XWPYN4S, B06XX2WQBN and the left-out cartridges: read through Amazon’s product data, Oct 22, 2026.
Google results for “kohler shower cartridge”: seen Oct 22, 2026. Search volume from Semrush, Oct 22, 2026.
