Boiler cycle rate and min on time with DHW kit - Y plan

[Adski]

Hi all,

I had the evohome system up and running for a few days before I could be bothered to install the DHW kit and all was good.
Due to the slightly awkward config for the DHW I no longer have a "boiler relay" and as such can no longer control the boiler cycles per hour and minimum on duration.
I know it's due to the proportional control algorithm but the boiler now occasionally fires for such an small insignificant time period it does nothing but annoy me...is there anything I can do to bring back the usual Honeywell options I've become accustomed to with the evohome and cm907 before that?

Thanks,
Adam

[Adski]

After much googling and finding unrelated topics I've ordered another relay to act as the boiler relay. I'm planning for this to be connected to L+N only and not actually control anything, but as it will hopefully on in tandem with the other relays will mean I'll have the boiler cycle and min on time options again.
Feel free to post if I'm barking up the wrong tree. I'll post again regardless once it arrives and with the result so it may help others in the future.

Adam

[Richard]

Hi Adam,

A 'boiler control' BDR91 will allow the cycle rates and minimum on time to be set differently to the default (6 cycles per hour and 1 minute minimum on time).

However, on a Y Plan & S Plan (when the BDR91 is setup and bound as a 'heating valve actuator') the BDR91 will follow a 6 cycles per hour and 1 minute minimum run time.

So if you have a modern domestic gas boiler, then it is perfectly alright to run at the 'default'. If you have an oil fired boiler or Heat Pump, then they will need to be set differently.

If you do use a 'boiler control' BDR91 for control of the boiler, just remember to negate the orange motorised zone wires as they are not required (and will cause issues with the TPI control if you do).

I hope that helps.

Richard.

[Adski]

Hi Richard.

Thanks for the info. I don't plan on wiring in the relay in to the heating electronics, literally just live and neutral purely so it'll unlock the additional software options hidden by the DHW installation.
Shouldn't really need hardware to overcome a software limitation, but hopefully it'll do the trick.

I've an oldish boiler with a cast iron heat exchanger and one minute of boiler on time will run barely warm water around the house for three minutes which is kinda pointless and it'd rather save the wear and tear on the old girl!

cheers