Ideal Logic+ Boiler- Pump Overrun

[Roy Martin]

Hi,

My ideal Logic+ boiler keeps displaying pump overrun while it is meant to be heating.

I've read in other places this is a normal function when the heating has been on and has just stopped. However, for me it keeps appearing during the time the boiler is meant to be on.

The radiators still heat up and get hot enough, but when the pump overrun appears they start to cool down even though the heating should still be on. It's keep coming on and off intermittently during this period. Can anybody advise why this would be happening and what the problem is?

 

[stem]

The heating could be selected to be 'on', but if the house has warmed up and reached the temperature set on the room thermostat, then the room thermostat will turn off the heating, and the pump overrun will operate. That's as it should be.

On the other hand, if the pump overrun is showing when the heating is selected 'on' and the room thermostat is calling for heat. Something is amiss.

 

[Mottie]

The heating could be selected to be 'on', but if the house has warmed up and reached the temperature set on the room thermostat, then the room thermostat will turn off the heating, and the pump overrun will operate. That's as it should be.

On the other hand, if the pump overrun is showing when the heating is selected 'on' and the room thermostat is calling for heat. Something is amiss.

Not always. On my system, with a Honeywell DT90E room stat, as my room temperature starts to get within 1 degree of the target temperature, it will shut the boiler down but the pump keeps running for a few minutes, it then fires up and repeats that boiler shutdown and pump overrun at 0.5 degrees before target temperature and then finally shutting down and doing a final pump overrun when it hits the target temperature. I thought that was wrong and contacted Honeywell and they told me that was a design feature to prevent the room reaching target temperature, shutting the boiler down with heat still coming from the radiator and then overshooting the target by a couple of degrees. It then fires the boiler every 10 mins or so for a couple of minutes to keep the room temperature stable. My stat rarely goes above .5 of a degree above the set temperature. Takes a little while longer for the room to reach target temperature from a cold start but much better than my old analogue room stat that would overshoot by a couple of degrees then had to get a couple of degrees below target temperature before switching the boiler back on.

 

[stem]

as my room temperature starts to get within 1 degree of the target temperature, it will shut the boiler down but the pump keeps running for a few minutes.

Isn't that pump overrun though? The heating is set to be 'on' but the thermostat has switched off boiler stops firing, but the pump continues.

The DT90E only has one set of contacts, so it will turn the boiler on /off, if the pump continues it must be the boiler pump overrun that is keeping it going.

 

[Mottie]

Isn't that pump overrun though? The heating is set to be 'on' but the thermostat has switched off boiler stops firing, but the pump continues.

The DT90E only has one set of contacts, so it will turn the boiler on /off, if the pump continues it must be the boiler pump overrun that is keeping it going.

All I know is what I was told by Honeywell. I think it's the 'proportional bandwidth' setting. I got this from the online installer instructions.

"Proportional band width: The proportional band is the temperature band, adjacent to the set temperature point, within which the thermostat will cycle the controlled output (to control the boiler, for example). Above or below this band the output will either be fully on or fully off. The band can be adjusted up to 3°C (default 1.5°C) to provide improved temperature control. This is useful for (a) well-insulated homes with over-sized heating systems or (b) air systems with a fast response".

So, the stat turns the boiler off within this band on it's wat to reaching the target temperature but the boiler makes the pump overrun to protect it from a sudden shutdown, if that makes sense?