Why does my gas boiler run when the house is warmer than the set temp?

I have an older high efficiency gas boiler and have had it and the thermostat inspected within the last few years. The thermostat is an analog dial. The house has radiator heat. The boiler kicks on intermittently when the thermostat shows that the house is 4-5 degrees above the set temperature.

Is this a design feature of high efficiency boilers since it may take a while to bring the house up to temp with radiators or is there something wrong with the thermostat or boiler control? Last night I fired my woodstove and could hear the boiler run for a long time although the tstat was set on 64 and its thermometer showed 70. The boiler wouldn't shut off until I turned the tstat down to 60.

One thing that comes to mind - is your analog dial one of the old Honeywell's with the mercury switch inside?

If it is and its not perfectly level it could be misreading the temperature by that much.

Yes it probably is. I had it adjusted once but it must not have helped. I can get a new one but want to make sure it is worth the spend.

In that case I'd strongly recommend updating to a digital programmable T-stat. More accurate and you can program setbacks by time and day of week. You should be ably to get a decent one under $50.

Was it actually transferring heart to the radiators or was the boiler just keeping the water I'm the boiler warm? Or is it a cold start boiler?

Does your boiler control have a low limit?

If it does, it will maintain a low limit (Usually 140 or 160), to ensure that the boiler is always hot.

Now if your pump is running, then the house thermostat is probably going bad.

That's what I was getting at. Maybe the boiler is just maintaining temp. OP may not have a pump. (gravity hot water out stream system)

It does have a pump and I don't think it is maintaining low temp because I turned it way down and it hasn't run for hours.

Is the pump on when it is running?

Funny, my oil fired boiler running on the old Honeywells started doing the exact same thing....

I brought this back because it's February and it's still doing this. It has an electric pump but I cannot tell if it is running. The boiler thermometer only reads about 100 degrees and the pipes leading from it don't feel as warm as they once did. The indicator lights on the boiler control panel are not indicating any errors.

This past summer I had to drain the water to remove a radiator during a bathroom rehab. I refilled it OK and don't think that much air is in there. The boiler has a sticker that says that "adding water will shorten the service life" - what gives?

Does the boiler heat your domestic hot water? if so, it will run when tap water needs heating.

There are really only a few reasons your boiler should run...

Thermostat calling for heat.

Hot water tank thermostat calling for heat.

You have a low limit on the boiler which calls for heat. (This is set on the boilers controller, this keeps the boiler warm for when heat calls)

If the pump is running it will vibrate. Feel or listen for the vibrations.

Look up the owners manual for your aqua stat. Find out what settings it has and what they are set at. Without this information we are only guessing at what might be the issue.

Matt

the Honeywell round t-stats have 2 pins under the cover that you set a level on and adjust by loosening the screw in the slot and moving the whole unit. Easy as pie. If it has been hit (really hit) to the point the spring or vile have been tweaked, save your self some grief and replace it.