Thermostat Not Dropping Quickly Enough

[Mark777]

Hi

I live in elderly sheltered property and have nothing but trouble with thermostat. I’m a bit confused. When i put it on 19 degrees intuitively i would say that when it reaches 19 it would turn off the boiler. But it goes to 20 before the boiler switches off. You now have to wait for it to drop to 19 before it comes on again, i assumed. But on reaching 19 it still did not come on. It came on at 18.5 degrees.

The problem is this took 4 hours 10 minutes despite the bungalow going cold long before this. In fact it was cold within 30 minutes. We end up having to turn the thermostat up a degree to make it come back on again. But when it gets to 21 degrees it’s back to square one because it will now take a long time for it to drop back down and come on. So we have to turn it up again!

Is this normal or am I misunderstanding something? Surely the purpose of the thermostat is to maintain a warm temperature throughout the day? We had a similar problem with the previous analogue thermostat which would click on and off around 15 degrees even though it was warmer than that. The new thermostat in the last couple of weeks is digital as we thought it would give us more control.

Am i expecting too much in thinking that it just cycles on and off every few minutes to maintain 19 degrees? What ive ended up doing is exploring various temperatures on the boiler even going quite low (40) to compare warmth and cost. Now it just comes on and stays on cycling between burner on and condensing. Im now looking at manually turning it off for 10 minutes or so throught the evening to see if that uses less or more gas.

I notice the install menu the engineer chose fast (F) to reach set point. I wonder if Slow would make any difference.

Many thanks.

Mark

 

[Mark777]

Hi

Seems to have resolved itself. Noticed the battery compartment wasn't fully pushed in. Since then it's now doing what i hoped it would. Still don't know if it will take too long for temperature to drop before it turns back on. I'm assuming it gets to the setpoint and maintains temperature but if it gets to 0.5 above setpoint i'm wondering if it will have to go down before boiler fires up even if it's getting a bit cold.

Thanks.

 

[Chuck]

My first thought is that although your radiators are coming on and off under the control of the thermostat they are not emitting enough power when they do. This could be because the flow temperature on the boiler is too low and/or or the pump that circulates the water is set too low or failing and/or the radiators have not been 'balanced' correctly.

To start with, I think some more details about your system would be helpful here. E.g., do you have panel radiators or underfloor heating? How many radiators in total. Do the radiators have individual thermostatic valves fitted to them. Are any radiators turned down/off? Can you tell us what make / model the thermostat is? Does the property have its own boiler, if so what make / model / age?

 

[milleniumaire]

Hi

Seems to have resolved itself. Noticed the battery compartment wasn't fully pushed in. Since then it's now doing what i hoped it would. Still don't know if it will take too long for temperature to drop before it turns back on. I'm assuming it gets to the setpoint and maintains temperature but if it gets to 0.5 above setpoint i'm wondering if it will have to go down before boiler fires up even if it's getting a bit cold.

Thanks.

I did wonder if maybe the boiler wasn't actually working off the thermostat and instead was reaching a set back temperature before it starts up?

 

[Chuck]

Based on the information in post #1, my guess is that the problem has three elements: Firstly, low circulation which is responsible for the slow heating. Secondly, the thermostat seems to be using on-off control (as opposed to TPI), which is responsible for the hysteresis. Finally, the OP is noticing the difference between 'thermal comfort' and 'air temperature' and feeling cold during the period when the radiators are off because the lack of radiant heat in the room reduces the 'thermal comfort'.

I didn't see post #2 before I wrote post #3. If reseating the batteries in the the stat hasn't fixed the problems then I'm sure we can help further given a few more details and a few rounds of Q&A.