Boiler stays on when thermostat temperature is satisfied

[Bunny Laroche]

Hello,

We have a new hot water heating system driven by ModCon boiler. So far we are very pleased with our system. We have, however, noticed that our upstairs zone's thermostat remains in a call for heat condition for a long period after its set temperature (70F) is satisfied. I believe this is actually a good thing, as it appears the longer the boiler runs the better (more efficient). But it remains curious why the thermostat remains in a state calling for heat even when it displays its ambient temperature of 70F has been satisfied.

The temperature never does go above the desired setting of 70F, and so this question is merely one of curiosity rather than concern.

 

[NY_Rob]

If it's a electronic t-stat, it may be a timer function programmed in to prevent 'bounce' where as soon as the heat call ends the air around the t-stat quickly cools and calls for heat again- so they have the relay stay closed for a bit longer rather than open as soon as the setpoint is reached.

If it's an old mechanical t-stat it's likely due to the 'anticipator': http://inspectapedia.com/heat/Heat_Anticipator_Adustment.php

In either case- it's beneficial to your boiler's long term health.

 

[Sponsor]

 

[Dana]

With some thermostats the differential or "dead zone" between the initial call for heat & the turn-off temp is programmable. Most non-programmable ones operate within about a 1-2F window, not calling for heat until it's at least a half degree below the set point, not turning off until it's a half degree or so above the set point.