Help - getting backflow to radiators when hot water on

[dave618249]

So system has been idle for 3 months but when I restarted it this week I have noticed the top floor radiators are heating up when the hot water is on. Simple I thought, just a stuck diverter valve, but no that is all working fine.

Through testing I can see that the both the CH and DHW diverters are working as they should (S-plan with closed/pressurised system) and that the top floor radiators are heating up via the boiler return (not the flow) and only the top floor, (ground floor radiators do not heat up). The DHW return is correctly piped as the last T before the boiler on the return. This was working fine until this week and there have been no changes to the system for quite some time so I am stuck for what the fault could be.

I have a Rehema Avante 24c boiler. The pump within the boiler appears to be working ok as the water is clearly flowing through the flow and return to both the hot water tank and the heating when I turn that on as well. I am thinking there might be some other flow sensor at fault. any ideas?

 

[CBW]

Possible wiring issue? Maybe it’s energising the heating zone valve or at least passing when dhw demand calling?

 

[dave618249]

thanks Chris, but I don't think this is a wiring issue. My tests show all valves operating as they should.

 

[dal5band]

Reduce the HW on time to a minimum to reduce the effect. I had to put TRVs in all the upstair radiators. Just happens in some systems, a convection current finds its way round.

 

[oldbutnotdead]

Injector Ts used to be fitted to prevent that problem