Blocking diode for radiator pump?

[Lucien Nunes]

Connect the heating pump in parallel with the heating valve motor blue and brown, and leave the heating valve orange output just energising the boiler and circulating pump. That way the heating pump and valve will operate at the same time but the water valve will not backfeed the heating pump. If whatever thermostat is controlling the heating valve cannot handle the load of the pump then a relay will be needed, but with modern low wattage pumps it should be fine to connect directly,

 

[malthep]

Thanks for the replies.

It would be easier to show a diagram really!

The output of the boiler is a closed system.

The motorised valves have the orange return line that powers the CH pump regardless of the CH or HW demand and also sends the demand to the boiler to turn on.

What I’d like is for the CH pump to only run when the CH valve is open. Problem still is there is only 1 wire to the boiler to demand heat regardless of the type of heating required (I.e CH or HW)

 

[brianmoooore]

If I've have this right, I think what you really need is a 2 port valve with two microswitches. AFAIK, these don't exist, so you will need the switch connected to both the pump and a small relay, which is used to turn on the boiler.

 

[Lucien Nunes]

What is wrong with my suggestion in post 11?

 

[Aaron b]

What is wrong with my suggestion in post 11?

I was suggesting the same, you put it more elegantly though .

 

[malthep]

View attachment 94625
I was assuming something like the sketch. I was thinking the heating signal would open the valve and turn on the room heating pump. The hot water signal through the stat would open the hot water valve. The contacts in either valves would turn on the boiler and pump.

Hi Aaron

Yes I think this sketch is pretty much correct. There is no pump on the boiler side but I assume there is one inside the boiler.

If you imagine that the two valves have the micro switch return power line connected together and then linked to the CH recirc pump and the boiler that is the the setup.

I need to isolate the micro switch returns and only power the CH pump when there is a demand for CH and not just HW.

Lucien has a great idea and if I’m right in interpretation I should link the CH pump with the activation signal to the motorised valve and not to the return wire?

 

[brianmoooore]

What is wrong with my suggestion in post 11?

Nothing whatsoever, other than I didn't read it before posting.

 

[Lucien Nunes]

That wasn't aimed at you, rather at the OP who I don't think had seen it either. It is the simple solution. As you say it is also possible to fire the boiler via a relay controlled by the valve microswitch, with its coil in parallel with the pump motor. But in this case it is unnecessary because the heating pump is in the secondary circulation and not throttled by the valve which is in the primary. Therefore it is not a problem that the pump will start at the moment the valve begins to open instead of when it is fully open.

if I’m right in interpretation I should link the CH pump with the activation signal to the motorised valve and not to the return wire?

Exactly right.

 

[malthep]

Connect the heating pump in parallel with the heating valve motor blue and brown, and leave the heating valve orange output just energising the boiler and circulating pump. That way the heating pump and valve will operate at the same time but the water valve will not backfeed the heating pump. If whatever thermostat is controlling the heating valve cannot handle the load of the pump then a relay will be needed, but with modern low wattage pumps it should be fine to connect directly,

Hi Lucien

Thanks for the reply, apologies in the delay in responding.

Am I

That wasn't aimed at you, rather at the OP who I don't think had seen it either. It is the simple solution. As you say it is also possible to fire the boiler via a relay controlled by the valve microswitch, with its coil in parallel with the pump motor. But in this case it is unnecessary because the heating pump is in the secondary circulation and not throttled by the valve which is in the primary. Therefore it is not a problem that the pump will start at the moment the valve begins to open instead of when it is fully open.



Exactly right.

perfect, I have done the wiring change…seems to be working correctly!

Many thanks

I’ll update this post if anything changes but my most sincere thanks to all, esp Lucien and Aaron