Vaillant boiler change in operation

[Dunbar]

Stat is Honeywell T4360. Need a bit of time to try and work out answers to questions in post 7. Thanks for info so far.

Not sure if relevant and/or whether it might point to the room stat as issue, but boiler fires up and stays on until temp reached for hot water.

 

[Basher]

Not sure if relevant and/or whether it might point to the room stat as issue, but boiler fires up and stays on until temp reached for hot water.

That Honeywell stat has a number of versions/options (I think there's a letter at the end of the serial number indicating which), and one version has a "heat anticipator" the exact operation of which I don't understand. It might be the little resistor (heater) found in some thermostats to reduce the hysteresis of the sensor. Could that be contributing to the issue - it shouldn't I guess?

 

[John.g]

Yes, that's how the anticipator works, if the stat is knocking off the boiler then the pump will run for the d.1 the overrun set time if it's going into anticycle then the anticycle time is set in d.2 there is also a s parameter telling you if its overrun or anticycle. The remaining anticycle time will also be displayed in one of the d parameters I think, if boiler is in recycle, remaining anticycle time is shown in d.67.
d.1 overrun defaults to 5 minutes, the anticycle actual time is per table, below, if thehe target temp is 75C then the annticycle time is 1 min irrespective of the set time which has a default setting of 20, apart from setting 1 (min) which strangley enough gives a actual anticycle time of 2 minutes.

 

[Dunbar]

Thanks for all replies. I thought I was out of warranty, but on checking, I have till March. Called Vaillant engineer out, who fitted new pcb and flow and return sensors which appears to have fixed early recycling issue.