boiler can't reach the temperature

rlxyz0

Hi,

I have an old Utica MCB125HD gas boiler. Recently found that the boiler can't reach the temperature set by room thermostat.

By doing some testing, I found that the boiler ran for about 2+ to 5+ minutes and then stopped when the temperature on the boiler reached 195-205F. After about 10 something minutes when temperature cooled down to about 160-170F, the boiler would start again.
The boiler just kept going in this cycle. The pressure was about the same when the boiler is cold and hot (see attached pictures). The Taco 007-FS calculator pump, replaced about 2 years ago, was sometimes a little more than warm (touchable).

Any help appreciated.

Eastman

What heats the rooms the thermostat serves? Radiators? Fintube? Do they heat up?

rlxyz0

there are baseboards in rooms and they all heat up. but the temperature can not reach to the temperature set . thanks

Eastman

What do you mean they heat up? How hot is the tubing that feeds the baseboard?

hot_rod

if the boiler reaches temperature and shuts down, then you have a circulation issue.

Bad pump or control that starts it

Air lock

Plugged strainer

Frozen pipes

Can you read the pressure on the lowers scale? should be 12 psi or more.

If the gauge works.

109A_5

Can you clean that gauge, can't see the lower Blue scale very well.

My bet from here is the system pressure its too low or the system is air bound, assuming the circulator is working properly.

The boiler is just cycling on the high limit since the heat is not being transferred to the rooms properly.

hot_rod

the chrome ring on the gauge should pop off, then you can remove and the glass with vinegar or CLR

When a gauge goes bad they often have rust and scale on the backside of the glass.

HomerJSmith

No flow or no heat transfer. To put it succinctly high delta T or too low delta T.

rlxyz0

let the system ran overnight and set the zone 1 at 68F and zone 2 at 73F. checked in the morning, the zone 1 reached 68F, but the zone 2 was at 63F. so maybe air in the zone 2? I didn't hear water sounds in the zone 2. thanks for all the help

Alan (California Radiant) Forbes

Maybe something going on with the baseboard. Make sure

• the damper is fully open
• the 2" of air space along the bottom is unobstructed
• the fins are clean

If you don't get proper air movement, the room won't heat up.

Also, you may not have enough baseboard to heat the room on a cold day. What are the dimensions of the room and how long is the baseboard?

HVACNUT

Show the whole boiler and piping around it.

rlxyz0

here is the whole boiler picture.

we only noticed the temperature issue recently. It was working ok last winter and earlier this winter.

HomerJSmith

Are those two blue valves below the red drain valves or the one below the Honeywell ZV fully open?

Which one is zone 2?

If it is the 571 zone valve, you can open it up by pushing the lever down.

rlxyz0

the one on the right is zone 2. the middle one is zone 1. the one on the left is another zone to basement. All the blue valves are fully open. I think the 571 zone valves are working properly as the pipes above them are very hot. Also the damper had been manually set fully open.

thanks

rick in Alaska

I agree with the others. Cut out the mixing valve, tie the manifold directly to the boiler, and let the boiler adjust the temperature. You apparently have it set up so the boiler is running 180 degrees to feed the mixing valve, so if you get rid of the mixing valve and let the boiler set the temperature, you can run the boiler at a lot less temperature, and your efficiency and cost of operation will be a lot better. That boiler runs best at lower temperatures.

Rick

109A_5

https://forum.heatinghelp.com/discussion/comment/1876398#Comment_1876398

@rick in Alaska how is this applicable to this thread ?

mattmia2

what makes you think the circulator is actually running? that relay has a tendency to break the solder joints on the relay after a few decades. the water in the boiler will make the circulator hot in that position. you can check for power at the circulator with a voltmeter. you can also try plugging it in with a test cord.

gravity circulation will get some heat to the emitters without the circulator.

it also looks like those auto vents are leaking. is the cap closed to stop the leak and also stopping them from venting air?

rick in Alaska

https://forum.heatinghelp.com/discussion/comment/1876400#Comment_1876400

I was posting on another thread. not sure how it made it here. Did not even see this post.

Rick

mattmia2

https://forum.heatinghelp.com/discussion/comment/1876407#Comment_1876407

i've had that happen before