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lazy-riders

Hopefully someone can help me out please. We have installed a biomass system which feeds multiple properties. Each property has an s plan system. A 2 core signal cable is connected to the orange and brown cable on the 2 port valve at each property which sends a volt free signal back to the biomass controller via a junction box to indicate a demand. This then sends a 230V signal to a contactor which turns on the district pump.

This all works fine apart from the biomass controller has an overun of 10mins for the district pump (which cannot be disabled as boiler will go into fault) and unfortunately because of RHI we cannot fit a bypass on the system.

So the workaround is to fit a relay that will switch the district pump off as soon as there is no demand signal from the 2 port valves. The signal sent from the biomass controller to 2 port valve when measured was 1.8v dc or 2.4v ac?

My question is what relay could I use (an RS product code would be helpful) and how would I connect it as i've not had much to do with relays before.

Wiring diagram is here

View image: Wiring

Thanks for your help.
 
Why do you want to stop the pump run on, it's there to prevent the boiler overheating when the demand from the valves stops?

How do you get circulation when the pump is on overrun and all the valves are closed if there's no by pass?

As it's a new/recent install it must have a smart circulation pump fitted which will reduce it's output as demand falls away
 
At the moment there is a bypass in the last property, however this has to be removed as the heat meter which is used to determine RHI payments will not reflect as it should.

There is a large accumulator tank which can take the excess heat to prevent boiler from overheating.

The district pump is a smart circulation pump which as the demand in each property reduces / the pump output ramps down.

Therefore as we need to remove the bypass the only option left is when there is no demand from any of the 2 ports is to switch the district pump off but still allow the boiler to dump excess heat into the 1500L accumulator tank.

Hope this makes sense.
 
My method would be to disconnect the zone valve contact circuit from the biomass input and use it to control two relays instead (coils in parallel) fed from a small local power supply unit at say 24V. One relay would have a normally open contact to feed the biomass input and the other similar to control the pump contactor, providing suitable isolation between the biomass ELV and pump LV circuits. It might be possible to combine both functions in one relay but there is the important matter of electrical separation between poles if the ELV circuit requires it.
 
Is the manufacturers design of the controller to have the 10 minute overrun? If so then you may invalidate any warranties etc if you bypass it.
 
I think the idea is to let the boiler and its pump overrun as intended (dumping the heat into a reservoir), but to run the district pump only during CFH. At the moment it also overruns because it is controlled via the boiler.
 
You don't need anything special, just a relay that can switch 230V for the contactor with a 24V coil (or whatever voltage you choose to send round the stat circuit) and a suitable degree of isolation between the two.
 

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