Boiler shutting off before reaching temp

AlwaysLearning2024 · January 26

Hi Everyone,

noticing a new issue with my WM cg-8 boiler. Reverse return hydronic with fin tube.

The boiler starts and runs just fine yet once the temp hits roughly 155 degrees, the boiler shuts off, flue dampener closes. Even though the Delmar 256 says keep going. And then doesn’t fire again until the temp drops to around 130.

the tekmar 256 shows “fire” during this shut off time, yet the boiler doesn’t fire.

if I manually power cycle the boiler, I can get the boiler to fire.

I’’m assuming there is some safely switch that may be tripping once 155 ish is being hit?

The high limit on the boiler itself is 180.

Pressure is good.

thanks for any help,

tcassano87 · January 26

Have you had a plumber come out and look at it, does it ever turn back on or does it stay off until you power cycle?

If it turns back on but it's reaching temp your temperature probe could be reading incorrectly, need to test the OHMS and compare it to Weil-Mclains chart to see what temp it thinks the boiler is at. If thats reading correctly could also be a problem with the board

AlwaysLearning2024 · January 26

thanks @tcassano87 .Tech hopefully coming out today. It does fire up without the power cycle but the temp drops before this can happen.

hot_rod · January 26

What are the boilers aquastat settings? It could be they are set low and turning off even though the tekmar is calling.

AlwaysLearning2024 · January 26

Thanks @hot_rod. Just a high limit on this one which is set to 180. (510-312-250).

The Relay buzzes a bit, too.

HVACNUT · January 26

Do you know actual supply water temperature? When the boiler shuts down and after the damper closes, jump the limit and see if it cycles back on.

AlwaysLearning2024 · January 26

@HVACNUT ! Thank you!

I jumped the high limit and it fired right up.

I rotated the high limit dial a few times to maybe dislodge some bits. Testing now.

Maybe best to grab a replacement?

Thank you!

AlwaysLearning2024 · January 29

I replaced the high limit yet still having the issue.

I'm now down to possible a flow issue??

The supply is about 20 degrees higher than the return (I'm just using a digital infared temp device).

The tekmar has a target of 173 and the boiler shuts off at 162 or so, yet the tekmar shows that it is still firing.

The boiler only starts back up again when the 30 degree differential from the high limit is met.

The limit is set to 180.

The temp/pressure gauge on the boiler corresponds within a few degrees to the tekmar pipe sensor.

Heat is being delivered to all of the heat emitters although the return of each is cooler.

If I jump the high limit, the boiler fire up when the tekmar is tellijng it to fire, yet I haven't tried to crank the high limit and see if the tekmar shuts the boiler off at the target temp.

Thanks for any help everyone!

HVACNUT · January 30

Do you have a probe thermometer or a K Type thermocouple you can put in the well to get a reading there? If the aquastat is the Resideo L4080B, they are notoriously inaccurate.

If you're up to it, you can clean the water side of the well and see if that makes a difference.

tcassano87 · January 30

out of curiosity did you put heat conductive compound on the probe?

AlwaysLearning2024 · January 30

Thanks @tcassano87 ad @HVACNUT.

I did not out any paste on the probe. Which pase would you recommend, @tcassano87 ?

Trying a probe thermometer soon.

hot_rod · January 30

Home Depot, Menards, Auto Parts stores usually have small squeeze tube of heat transfer paste.

HD example

tcassano87 · January 30

yeah like hot rod said there are a few different types. Honeywell, white Rodgers makes them. They come in single use or like a tub. Might not solve the issue but those aquastats are inaccurate and that could be an inexpensive way to help the situation

Boiler shutting off before reaching temp

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