Get the Winters TTD404, 9.6 on our spec score: a tridicator for a 1/4-inch back tapping, with a five-year warranty. A 1/2-inch bottom tapping takes the Dwyer TRI2-60-50L. Most homes read about 12 psi cold.
Top pick: Winters TTD404$22.87 at AmazonPrice as of Oct 24, 2026, 5:30 AM EDT
All tridicators, which read boiler pressure and water temperature on one dial. Each was new and in stock on Amazon as of Oct 22, 2026, and each scores 7.0 or higher on our spec score.
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 each maker’s data sheet and warranty terms, equal weight. The rules and every input are in the method section near the end.
PlumbingPicks spec score out of 10, from the makers’ data sheets and warranty terms, read Oct 22, 2026. It is not a customer rating or a lab test of our own.
A boiler pressure gauge on a hot-water heating system is almost always a tridicator. One needle reads system pressure and the other reads water temperature, so the boiler needs only one tapping. Trerice’s data sheet puts it plainly: tridicators are designed specifically for hot-water boilers.
All three picks are Grade B gauges, ±3-2-3% on pressure. So the score splits them on what else each maker puts in writing: temperature accuracy, a boiler code statement, the warranty, the units on the dial and how many ways it can be fitted.
Each pick, in detail
What each maker publishes, which boiler tapping each one fits, and where each one lost points on our checks.
Best for a 1/4-in. back tapping
Winters TTD404
Tridicator, 2.5 in. dial, 1/4 in. NPT back, 2 in. stem, 0–75 psi, 70–320°F
Ranges stated to comply with ASME Section IV HG-612
Five-year warranty
Three 2.5-in. fittings in Winters’ table
Cons
psi and kPa only, no feet of water
Pressure limit is 75% of full scale
California Prop 65 warning names lead
2.5 in. dial1/4 in. NPT back2 in. stem0–75 psi70–320°F
Buy it if
Your boiler has a 1/4-inch tapping where the old gauge screws straight in from the back, and you want the gauge with the most published facts behind it.
Skip it if
The tapping is 1/2 inch, or it points up from below the dial. The Dwyer TRI2-60-50L fits a 1/2-inch bottom tapping.
The TTD404 is Winters Instruments’ 2.5-inch tridicator, and I’ve used it. The top scale reads boiler pressure from 0 to 75 psi, with kPa in red. The bottom scale reads water temperature from 70 to 320°F, with Celsius in red. It scored 9.6, the highest of the three.
Winters puts more in writing than the other two makers. It gives pressure accuracy as ±3-2-3% and temperature accuracy as ±3% of full scale, a 10. The data sheet also says its ranges comply with ASME Boiler Code Section IV HG-612, another 10. Neither Dwyer nor PIC put a code statement on their sheets.
The warranty is five years, printed on the same data sheet, and that’s a 10. Dwyer’s and PIC’s terms run one year from delivery.
Fit options are where the TTD line helps on a replacement job. Winters’ 2.5-inch table has three 0 to 75 psi versions: the TTD410 with a 1-inch stem, this TTD404 with a 2-inch stem, and the TTD401 with an extension back that pairs with Winters’ TST025 thermowell. Three options scored a 10.
The one check it lost is units. The dial reads psi and kPa, with no feet of water, so it’s an 8. If your boiler manual gives pressure in feet, divide feet by 2.31 to get psi.
Inside, the socket and stem are brass, and the Bourdon tube that moves the pressure needle is phosphor bronze. Temperature comes from a bimetal coil. The case is steel painted black, and the 2.5-inch lens is threaded acrylic.
Winters rates it for ambient air from 23 to 122°F and lists an IP50 enclosure. It also sets a pressure limit of 75% of full scale, about 56 psi on this dial. That sits well above the 30 psi relief valve setting Amtrol uses in its boiler sizing tables.
Winters’ sheet lists hot-water and steam boilers as applications. Trerice says tridicators are built for hot water, and Weiss says steam gauges need a coil syphon. The steam section below shows what I’d use there.
My call: match the stem length to the old gauge before you order, so the new stem sits in the tapping the way the old one did. Winters makes the same dial with a 1-inch stem for shallow tappings.
Best for a 1/2-in. bottom tapping
Dwyer TRI2-60-50L
Tridicator, 3 in. dial, 1/2 in. NPT bottom, 0–60 psi, 80–290°F
Your boiler’s gauge tapping is 1/2 inch and points up, so the gauge screws in from the bottom of its case.
Skip it if
Your tapping is 1/4 inch through the boiler jacket. The Winters TTD404 or the PIC fit that.
The TRI2-60-50L is Dwyer Instruments’ 3-inch tridicator with a 1/2-inch NPT bottom connection, and I’ve used it. Pressure reads 0 to 60 psi, or 0 to 400 kPa, in blue. Temperature reads 80 to 290°F, or 30 to 140°C, in red. It scored 8.0.
Dwyer publishes both accuracy figures: pressure to ±3-2-3% and temperature to ±1 scale division. That separate temperature figure earned a 10, the same as Winters.
The TRI2 line comes three ways, and Dwyer makes the 0 to 60 psi range in all three: the 60-50L with a 1/2-inch bottom connection, the 60-50 with a 1/2-inch back connection, and the 60-25E with a 1/4-inch back connection on an extension shank. Three options scored a 10 on fit.
The 0 to 60 psi range has a real benefit on a home boiler. A Grade B gauge is most accurate in the middle half of its scale, which on this dial runs from 15 to 45 psi. A hot reading under a 30 psi relief setting can land there, and the error band in the middle is ±1.2 psi.
It lost points on paperwork. Dwyer’s TRI2 sheet makes no ASME Section IV statement, a 6. DwyerOmega’s warranty page gives one year from delivery unless a product sheet says otherwise, and the TRI2 sheet doesn’t, another 6.
Units are psi and kPa, so it’s an 8 there, the same as Winters. Dwyer rates the pressure limit at the full scale range, 60 psi, which is twice a typical 30 psi relief setting.
The wetted parts are a brass connection and a phosphor bronze Bourdon tube, in a drawn steel housing with a black finish. Dwyer gives the weight as 12.35 ounces, or 350 g, and ambient limits of −40 to 250°F. The sheet also lists NIST-traceable calibration certificates as order options, for jobs that need a paper trail.
My call: put this one where you’ll read it from across the boiler room. The 3-inch face is the largest of the three, and Dwyer prints pressure in blue and temperature in red, so the two scales are easy to tell apart.
Best for reading feet of water
PIC Gauges TRI-RC-254R1.75-D
Tridicator, 2.5 in. dial, 1/4 in. NPT back, 1.75 in. stem, 0–75 psi / 0–170 ft
2.5 in. dial1/4 in. NPT back1.75 in. stem0–75 psi / 0–170 ft70–320°F
Buy it if
Your boiler manual or the old gauge talks in feet of water or altitude, and you want a dial that reads it without the math.
Skip it if
You want the longer warranty and the code statement. The Winters TTD404 fits the same 1/4-inch back tapping.
The TRI-RC-254R1.75-D is PIC Gauges’ 2.5-inch tridicator with a 1.75-inch stem and a 1/4-inch NPT center back connection, and I’ve used it. PIC Gauges is a division of Engineered Specialty Products. It scored 7.6.
It’s here for the scale. Pressure reads 0 to 75 psi on one ring and 0 to 170 feet of water on the other. It’s the only pick that does, a 10 on units. Some boiler manuals give fill pressure in feet of water, and a gauge that reads feet is often called an altitude gauge.
PIC makes this dial with three stem lengths: 1.75, 2.95 and 3.63 inches. Three options scored a 10 on fit.
It lost points on what the sheet leaves out. PIC gives one accuracy line, 3-2-3% of full scale per Grade B in ASME B40.1, with no separate temperature figure, a 6. There’s no ASME Section IV range statement, another 6.
PIC’s terms of sale cover products it makes for 12 months from delivery, repair or replace at PIC’s choice, a 6 on warranty. Its sheet also notes that very high or low ambient temperatures may affect accuracy, and gives an ambient range of −30 to 180°F.
The build is a black painted steel case that isn’t made to be liquid-filled, a copper alloy stem and connection, and a plastic lens with a red indicator. In the listing photo the indicator is a red triangle at the edge of the temperature scale. A side photo in the listing shows “Made in China” on the case.
The brand-written listing says it’s available with a 1/2-inch NPT adapter, and PIC’s sheet lists special connection sizes as an option. Check what the listing ships with before you count on the adapter.
Temperature reads 70 to 320°F and 20 to 160°C, the same span as the Winters. PIC also makes the dial in 0 to 100 and 0 to 200 psi, for systems with higher relief settings.
My call: pick this one if you think about your system in feet of height. It turns the fill rule into a straight read on the dial.
The three side by side
Dial, connection, ranges, accuracy and paperwork, from each maker’s own data sheet.
From Winters’ TTD data sheet, Dwyer’s TRI2 sheet and DwyerOmega’s warranty page, and PIC Gauges’ 2.5-inch tridicator sheet and terms of sale, read Oct 22, 2026. FS means full scale.
Is your boiler pressure right?
Enter the height of your system and the gauge readings. The checker uses the fill rule from Lion Boilers’ installation manual.
The rule behind it is short. Lion Boilers’ CEB manual recommends a cold fill of 12 psi, which should leave at least 4 psi at the highest point in the system. Pressure drops 0.433 psi for every foot above the fill point. So 12 psi covers a system up to about 18 feet above the gauge.
Above that, add pressure. Take the height in feet, multiply by 0.433 and add 4. A 30-foot system needs about 17 psi cold.
Height from the gauge to the highest point of the system. Minimum cold fill is 12 psi or height × 0.433 + 4 psi, whichever is higher, from Lion Boilers’ CEB manual.
Height above the gauge
Minimum cold fill
In feet of water
Pressure left at the top
Up to 18 ft
12 psi
27.7 ft
4 psi or more
20 ft
12.7 psi
29.3 ft
4 psi
25 ft
14.8 psi
34.2 ft
4 psi
30 ft
17.0 psi
39.3 ft
4 psi
35 ft
19.2 psi
44.4 ft
4 psi
40 ft
21.3 psi
49.2 ft
4 psi
Feet of water is psi × 2.31, the inverse of Lion’s 0.433 psi per foot. Your boiler maker’s manual wins if it gives a different fill pressure.
Why the reading climbs when the boiler heats up
Hot water takes up more room than cold water, and the expansion tank is what keeps that from showing up as a spike on the gauge.
Lion’s manual says the expansion tank must allow for about 4% expansion of all the water in the system. A properly sized tank keeps the hot pressure from going past the recommended operating pressure.
Amtrol’s tank sizing tables for Fill-Trol and Extrol tanks assume a 12 psig fill and a 30 psig relief valve. Its newer Extrol PRO tables assume a 15 psig fill. Either way, the tank is chosen so the hot reading stays under the relief setting.
Reading
What it means
Source
12 psi cold
Normal for a system up to about 18 ft above the gauge
Lion CEB manual
15 psi cold
Amtrol’s fill basis for Extrol PRO sizing; Caleffi’s AutoFill factory setting
Amtrol, Caleffi
Hot, higher than cold
Normal: the expansion tank is taking up the 4% growth
Lion CEB manual
Hot, near 30 psi
Tank may be improperly charged or undersized
Amtrol manuals
30 psi
A typical relief valve setting in Amtrol’s sizing tables
Amtrol manuals
Caleffi’s 553 AutoFill valve, a common automatic fill valve, ships set to 15 psi and adjusts from 3 to 60 psi, accurate to ±2 psi. If your cold reading keeps coming back to one number after you drain some water, that’s the fill valve’s setting.
My call: if the hot reading creeps up over a season while the cold reading stays put, check the expansion tank’s air charge first. Amtrol ships its tanks at 12 psig and says to set the charge to match the system fill pressure.
How far off a Grade B dial can read
All three picks are Grade B: ±3% of full scale in the first and last quarter, ±2% in the middle half.
Worked from the Grade B rule in AMETEK U.S. Gauge’s application note: ±3% of full scale in the first quarter, ±2% in the middle half. 12 psi sits in the first quarter of both dials; 25 psi sits in the middle half.
AMETEK U.S. Gauge explains that the middle half of a Grade B gauge’s range is the most accurate, and that you should pick a gauge so the expected reading lands there. On a 0 to 75 psi dial the middle half runs from about 19 to 56 psi. On a 0 to 60 psi dial it runs from 15 to 45 psi.
So a 12 psi cold reading sits in the less accurate first quarter on both dials. A 0 to 75 psi gauge can read anywhere from about 10 to 14 psi and still be within its grade.
My call: don’t chase a half-psi difference between an old gauge and a new one. If they disagree by more than about 2 psi, check both against a test gauge on the boiler drain before you add or drain water.
Match the thread, the mount and the stem
Read these four things off the old gauge before you order. They decide which model fits, more than the brand does.
1/4 in. NPT is about 0.54 in. across the threads; 1/2 in. NPT about 0.84 in.
1/4 in. (Winters, PIC) or 1/2 in. (Dwyer)
Stem length
Measure from the thread to the tip
1 in. or 2 in. (Winters), 1.75, 2.95 or 3.63 in. (PIC)
Pipe thread sizes are nominal, so a 1/4-inch NPT thread measures about 0.54 inch across the outside, per the ASME B1.20.1 thread table. That’s why a “1/4-inch” gauge looks too big for the name. A 1/2-inch NPT thread measures about 0.84 inch.
The stem holds the temperature sensor. Many tridicators sit right in the boiler water. Some fit a thermowell, a fitting that stays in the boiler and holds the stem. Winters’ TTD401 is the version made for its TST025 thermowell.
My call: when the old gauge has a well, buy the gauge made for that well, or replace both together.
psi, feet of water, kPa and bar on one dial
Boiler gauges and manuals don’t all use the same unit. Here are the common readings in each.
psi
Feet of water
kPa
bar
4 psi
9.2 ft
27.6 kPa
0.28 bar
12 psi
27.7 ft
82.7 kPa
0.83 bar
15 psi
34.7 ft
103.4 kPa
1.03 bar
21.8 psi
50.4 ft
150 kPa
1.5 bar
30 psi
69.3 ft
206.8 kPa
2.07 bar
Feet of water use 2.31 feet per psi, from Lion’s 0.433 psi per foot. kPa use 6.895 kPa per psi, from NIST’s SI conversion guide, and 1 bar is 100 kPa, or about 14.5 psi. PIC prints 75 psi as 170 feet on its dial, a little under the 173 feet the factor gives, so read the dial’s own marks.
An altitude gauge is a boiler gauge that reads pressure in feet of water. Weiss sells its Tri-o-meter on the same idea: one instrument reads water pressure, temperature and system head in feet of H2O.
When the gauge reads too high or too low
Common readings, the usual cause, and what the boiler and tank makers say about them. Where the advice is mine, it’s marked as my call.
What you see
Likely cause
What to do
Cold reading under the minimum for your height
Water lost through a vent, valve or leak
Top up to the minimum (my call: then watch it for a week)
Pressure too high when hot
Defective expansion tank or fill valve, or the tank is too small
Lion CEB troubleshooting table
Relief valve dripping
Expansion tank improperly charged or undersized
Check the expansion tank (Lion, Amtrol)
Pressure falls a little every day
A slow leak or a weeping relief valve
My call: look for drips at valves and the relief outlet
Needle never moves
Stuck gauge or a plugged tapping
My call: compare with a test gauge on the boiler drain
A hose-thread test gauge on the boiler drain is the quickest way to tell if the dial is lying. Our water pressure gauge guide covers that kind of gauge. If the boiler gauge and the test gauge disagree by more than the Grade B band, replace the boiler gauge.
My call, step by step, for a tridicator that sits right in the boiler water. Follow your boiler maker’s manual where it says something different.
1
Shut it down and let it cool
Turn off power to the boiler and close the fill valve. Wait until the gauge reads well under 100°F before you open anything.
2
Drop the pressure
Open the boiler drain into a bucket until the gauge reads zero. If the tapping is low on the boiler, drain below the tapping.
3
Swap the gauge
Turn the old gauge out with a wrench on its hex, never the case. Seal the new threads with a sealant rated for hot water.
4
Refill and bleed
Open the fill valve, bring the cold pressure to the minimum for your height, and bleed the air from the top radiators.
5
Fire it and watch
Run the boiler to temperature and read the hot pressure. Check the new gauge’s threads for drips while it’s hot.
Work on a gas or oil boiler’s controls, venting or burner belongs to a licensed heating tech. Swapping a gauge doesn’t touch those.
Steam boilers take a different gauge
A tridicator is a hot-water gauge. Steam boilers need a pressure gauge that’s protected from the steam itself.
Source
What it says
Trerice tridicator sheet
Tridicators are designed specifically for use with hot-water boilers
Weiss gauge catalog
Steam service gauges should be protected by a coil syphon (SY14-S iron or SY14-B brass)
Winters TTD data sheet
Lists hot water and steam pressure for boilers as applications
The makers don’t agree on steam, so I show all three. A steam boiler runs at low pressure, and the gauge’s range should match what the boiler maker lists.
My call: on steam, buy the gauge the boiler maker specifies and mount it on a syphon, the loop of pipe that holds water between the steam and the gauge. None of the three picks here is a steam gauge.
Boiler gauges we checked and left out
These came up in Amazon searches on Oct 22, 2026. Here’s what kept each off the list.
Gauge
What we found
Why it’s out
Trerice PTC14201
Trerice’s sheet: 2.5 in., 1/4 in. rear with lag, 0–75 psi, HG-612, 3% temperature
Listing photo shows a different style of gauge
Weiss HTP40L
Weiss lists its HTP series at 0–200 psi
Listing photo shows a 0–75 psi dial with feet of water
Weil-McLain 510-218-099
Weil-McLain’s own combination gauge, “all boiler sizes”
Too little published to score
Unbranded “replacement for” gauges
Dozens of listings named after another maker’s part number
Not the brand they name
Trerice publishes the same facts Winters does, and Weiss makes a feet-of-water Tri-o-meter. But both Amazon listings show a photo that doesn’t match the model on the maker’s sheet, so I can’t tell which gauge would arrive.
If your boiler is a Weil-McLain and you want the factory part, its 510-218-099 is the exact swap. It just can’t be scored on maker specs, so it isn’t a pick here.
How to choose in five questions
Question
If yes
If no
Is the old gauge’s thread 1/4 in. on the back?
Winters TTD404 or PIC
Next question
Is the thread 1/2 in. on the bottom?
Dwyer TRI2-60-50L
Dwyer’s 60-50 (1/2 in. back) or a well-type gauge
Does your manual give pressure in feet?
PIC Gauges, with a feet scale
Winters or Dwyer
Do you want the longest warranty?
Winters, five years
Any of the three
Is it a steam boiler?
The boiler maker’s steam gauge on a syphon
A tridicator from this page
My call for most homes with a cast-iron or gas-fired hot-water boiler: the Winters TTD404 if the tapping is 1/4 inch on the back, the Dwyer TRI2-60-50L if it’s 1/2 inch on the bottom. Take the old gauge with you, or a photo of its side, before you order.
Questions people ask
What is the best boiler pressure gauge?
The Winters TTD404, at 9.6 on our spec score. Winters publishes both accuracy figures, an ASME Section IV range statement and a five-year warranty.
What should a boiler pressure gauge read?
About 12 psi cold for a system up to 18 feet above the gauge, per Lion Boilers’ manual. Taller systems need the height times 0.433 plus 4 psi.
What psi should a boiler be at when the heat is on?
Higher than the cold reading, and below the relief valve setting, often 30 psi. Amtrol sizes expansion tanks so it stays under that.
What happens if boiler pressure is too low?
The top of the system loses pressure. Lion’s manual asks for at least 4 psi at the highest point. My call: below that, air gets in and upstairs radiators go cold.
What type of pressure gauge is used on a boiler?
On a hot-water boiler, a tridicator, which reads pressure and temperature on one dial. Steam boilers use a pressure gauge on a coil syphon.
What is a tridicator?
A combination pressure and temperature gauge. Trerice says it needs only one access point to the boiler because one instrument reads both.
What is an altitude gauge on a boiler?
A gauge that reads pressure in feet of water. 1 psi is about 2.31 feet. The PIC Gauges pick reads both psi and feet.
Why does boiler pressure go up when it heats?
Water expands about 4% as it heats, per Lion’s manual. The expansion tank takes up that growth; if it can’t, the pressure climbs.
Why is my boiler relief valve dripping?
Amtrol says a dripping relief valve can mean the expansion tank is improperly charged or undersized. Lion’s troubleshooting table also says to check the tank.
How accurate is a boiler pressure gauge?
All three picks are Grade B, ±3-2-3%. On a 0 to 75 psi dial that’s up to ±2.25 psi near 12 psi and ±1.5 psi in the middle.
What is 1.5 bar in psi?
About 21.8 psi. One bar is 100 kPa, or about 14.5 psi.
Can I put a tridicator on a steam boiler?
Trerice says tridicators are designed for hot-water boilers, while Winters lists steam too. My call: use the boiler maker’s steam gauge on a syphon.
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 Winters’, Dwyer’s and PIC Gauges’ own data sheets and warranty terms, read Oct 22, 2026. Where I add advice of my own, it’s labeled as my call.
How I pick
Only tridicators for hot-water boilers from documented makers, new and in stock on Amazon, checked through Amazon’s product data the same day.
The model in the listing has to match the maker’s sheet, photo included. Two well-known gauges failed that check.
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 maker documents, not a customer rating or a lab test of our own.
Check (weight)
How it’s scored
Temp accuracy (⅕)
10 when the maker publishes a separate temperature accuracy; 6 when it doesn’t
Code range (⅕)
10 when the maker states its ranges comply with ASME Section IV HG-612; 6 when it doesn’t
Warranty (⅕)
10 for 3 years or more; 8 for 2 years; 6 for 1 year
Units (⅕)
10 for psi and feet of water; 8 for psi and kPa
Fit options (⅕)
Connection or stem options in the maker’s table for that dial: 10 for 3 or more; 8 for 2; 6 for 1
Total
Average of the checks, to one decimal
Pick
Temp accuracy
Code range
Warranty
Units
Fit options
Score
Winters TTD404
10 (±3% FS)
10 (HG-612)
10 (5 years)
8 (psi, kPa)
10 (3 versions)
9.6
Dwyer TRI2-60-50L
10 (±1 division)
6 (none)
6 (1 year)
8 (psi, kPa)
10 (3 mounts)
8.0
PIC Gauges TRI-RC-254R1.75-D
6 (not given)
6 (none)
6 (12 months)
10 (psi, feet)
10 (3 stems)
7.6
Sources
Winters Instruments, TTD Tridicator data sheet (pages 223–224): read Oct 22, 2026.
Dwyer Instruments, Series TRI2 Tridicator Gage data sheet, and DwyerOmega warranty policy page: read Oct 22, 2026.
PIC Gauges (Engineered Specialty Products), 2 1/2-inch Tridicators data sheet and Terms & Conditions, section 4.2: read Oct 22, 2026.
Trerice, Tridicator data sheet (models 140 to 146, page 145) and company guarantee page: read Oct 22, 2026.
Weiss Instruments, HVAC gauges and Tri-o-meters page and gauge catalog: read Oct 22, 2026.
Lion Boilers, CEB Series Boiler Installation Manual, V16.0: read Oct 22, 2026.
Amtrol, Fill-Trol, Extrol L Series and Extrol PRO installation and operating instructions: read Oct 22, 2026.
Caleffi, 553 series AutoFill submittal 02178-25 NA: read Oct 22, 2026.
AMETEK U.S. Gauge, application note on full scale vs. Grade B accuracy gauges: read Oct 22, 2026.
ASME B1.20.1 pipe thread outside diameters, and NIST Special Publication 811 conversion factors.
Brand-written Amazon listing text and item data for B0087VKZK4, B00E6G9KFK, B00FBQAPGW, B00G2585GI, B008FVET94, B01MUD3D49 and the left-out gauges: read through Amazon’s product data, Oct 22, 2026.
Google results for “boiler pressure gauge”: seen Oct 22, 2026. Search volumes from Semrush, Oct 22, 2026.
