3 loop S plan, converting to OT

[bn8959]

Hi
Im not certain on the optimum configuration for my system.

I currently have an S-plan system with 3 loops (DHW, heating and under-floor), each controlled by 2 port valves. All radiators have TRVs.

I have replaced my old boiler with an InterGas HRE OV.

Currently I have rewired the system so the boiler has permanent power, and the boiler powers the pump - pretty straight forward. I see that hot-water priority is recommended though and I am wondering how best to implement it. I could replace the heating 2 port valve with a N/O valve, but then I have the underfloor loop to consider (which is controlled by a HCC80R). I was thinking about wiring the valves using the N/C switched electrical output from the hot water 2 port valve to provide power to the heating and underfloor 2 port valve motors. Therefore when hot water is called, power to the other two valves will be removed and they will both close.
This would save me having to physically swap any valves. The only downside I can see is that I still need a BDR91 to switch the heating valve. I have my plumber here today and tomorrow, so I don't have much opportunity to change valves easily if necessary.

Thanks
Ben

[Richard]

Did you get this sorted Ben? Sorry I have only just seen this post...

[bn8959]

Hi
Well, I think I’m there. I have used the option of utilising the ‘white’ wire NC switch from the hot water two port valve to switch the neutral wire to the heating an underfloor two port valves, with the positive feeds fed respectively from the heating BDR91 and the heat demand output from the underfloor controller. This means that when there is hot water demand both the heating and hot water loops close - giving me hot water priority as recommended.

This all seems to work very well, but with one exception. The heating BDR91 doesn’t seem to activate as much as it should. The EvoHome controller is showing heat demand from the various radiator zones, (at a relatively low value) and opentherm is activating the boiler, but the heating BDR91 is off; meaning a lot of the time the boiler is just circulating warm water through the bypass value.
I can’t work out the logic why opentherm is activating the boiler but none of the 3 valves are open (and it runs like this for a lot of the time).
All my components have excellent signal and are all mounted as per spec (30cm gaps, no metal inc back boxes etc).

Do you have any idea why this may be? I don’t really want to have to swap out the heating valve for a NO type, and even then I’m not sure how that would play with my underfloor loop too.

Thanks
Ben