Munchkin T40M rumbles and vibrates when firing from low temp

nbereny

First time poster here, homeowner. CA, Bay Area.

Had the T40M Munchkin Boiler installed about 10 years ago to support radiant heating. It seems to definitely be struggling lately to hold temps when the temp drops outside to <40.

Recently, it has started rumbling and vibrating when it fires up at low temps.

The two use cases are:
1. Temperature on the boiler is around 70-90 in the early afternoon when the outside temperature is warmer. When the boiler fires up at this temperature late at night, it starts rumbling each time the boiler fires. And this goes on every minute or so, and can sometimes go for over an hour. When the temp reaches about 120, further firing does not seem to make the unit rumble. The sound is like a large truck stalling.

2. It seems to especially also happen when the temperature dips to <40. Not often in CA, but it still does. When the temp is around 40 +, the system does not seem to rumble.

The tech from the company who installed it came out and could not reproduce it because he comes in the morning when the temps are at 125 or 128. Turning unit on/off etc does not reproduce it.

Can this be fixed? Or is it time to replace the munchkin? I also reached out to HTP with this issue.

Help!

fenkel

Have you checked the fan assemble? Its made up with plastic and can wear out and wobble on start ups.
Any codes?

Zman

When is the last time it was disassembled and cleaned? Has a combustion analysis been performed recently?
Munchies are great little boilers, they need regular serving.

SuperTech

Zman said:

When is the last time it was disassembled and cleaned? Has a combustion analysis been performed recently? Munchies are great little boilers, they need regular serving.

This was my first thought as well.  These boilers are very maintenance sensitive.  They need to be properly cleaned and tuned annually. Combustion analysis is essential for providing reliable operation.

kcopp

The swirl plate inside may need to be replaced.

HomerJSmith

Did HTP make a T40M? What is the nameplate model #.

It's a combustion issue as Zman suggests. Clean it and do a combustion analysis on it with a recently calibrated CO meter.

Alan (California Radiant) Forbes

The rumbling sounds as though the gas/air mix is too rich and needs to be adjusted by someone that has a manometer.
I'm in Berkeley if you want to talk about it. (510)773-9870 cell

Munchkin boiler sizes are T50M, T80M, T140M and T199M.

HomerJSmith

I dug out an old manual and all I see is a T50M and a T80M.