S Plan with 2 Pumps 1 Pump 24/7

[Nibber]

Hello
I have an unvented S plan system with two pumps one for CH and the other for HW the hot water one runs continuously 24/7 is there any way it can be wired to turn on just when the HW is called
Thank you

 

[flameport]

Yes, that's the normal method.
If it's running 24/7 it's been wired incorrectly.

 

[dal5band]

Ah ! I have this system, it's not as simple as people may think to have full independant timer control ofthe HW and CH. The problem comes in seperating out the ON signals to the boiler. So that CH "on" signal does not turn the HW pump on and vise versa because they get connected together at the boiler. One way is to have a motorised valve in each circuit and use the valve relay to turn on the boiler but the pump in each side is connected to its respective thermostat and not to the valve relay. An alternate method would be to have relays in the circuits to isolate HW from CH side if one of them needs to be off. I have a relay onthe CH side and a valve in the HW side because you need that anyway to control the HW temperature. We do get some convection flow through the CH pump that heats some radiators upstairs but thay have TRVs so not a problem. This is a very old system which was in the house and i keep meaning to have it replumbed to a conventional one pump system but never got round to it. Probably happen when the boiler gets changed. Here's a picture of the pumps.

 

[ianmcd]

Motorised valves do not have relays, that is the whole point of fitting them, your system is not wired correctly

 

[Nibber]

Thanks for the replies, so is it as simple as finding where the circuit is to turn on the HW Motorised Valve in the wiring centre and wiring the pump into that circuit, or is that too simple\dangerous

 

[dal5band]

If your system is unvented then you need a proffesional as the high pressure HW systems can blow up if the HW overheats.
A motorised valve acts like a relay , the motor actuates a microswitch to switch through a voltage to the boiler.

 

[Nibber]

Thanks, I guess your right but it was a professional that wired it wrong in the first place, I guess they were NOT that professional

 

[dal5band]

Get youself an S plan diagram and mark in where your connections go - may help understand what's happening.

 

[Nibber]

This is my set up setup now as I removed the HW pump several years ago and switched it on and off via my automated Vera Plus network ie zwave so when the HW was called the plug automatically switched the pump on and off as necessary

Problem is I have just replaced the receiver and thermostat with a Nest which wont connect to my zwave network

So can someone give me a clue how to wire in the second pump for Hot Water please

Thanks

 

[oilhead]

Do you definitely have two primary circulating pumps, or is one a secondary DHW circulating pump?

 

[dal5band]

That looks like a normal S plan. When the HW thermostat calls for heat, the boiler and pump in the diagram will run. The orange wires from the two valves run the boiler+pump combo.

 

[Nibber]

Do you definitely have two primary circulating pumps, or is one a secondary DHW circulating pump?

I think you are right its must be a DHW circulating pump

So how could I wire that please

 

[ericmark]

It is common with hotels and large houses to circulate the hot water so there is no delay getting hot water out of the taps, is the hot water pump to do this?

I have a C plan with two central heating pumps, and the result is I need relays, with one pump the micro switch in the motorised valve works both the boiler and pump, but to get two motorised valves to only turn on one pump and boiler can't work, the boiler would auto link the pumps, so motorised valve turns on pump and relay and relay turns on the central heating boiler.

I would think if second pump circulates then there will be times when not required, so I would think a simple timer is all that is required. It is an interesting problem as if for example everyone washes in morning it is only needed for first person as once pipes hot they will stay hot.

 

[Nibber]

It is common with hotels and large houses to circulate the hot water so there is no delay getting hot water out of the taps, is the hot water pump to do this?

I have a C plan with two central heating pumps, and the result is I need relays, with one pump the micro switch in the motorised valve works both the boiler and pump, but to get two motorised valves to only turn on one pump and boiler can't work, the boiler would auto link the pumps, so motorised valve turns on pump and relay and relay turns on the central heating boiler.

Yes it is to circulate hot water, thanks

 

[ianmcd]

Yes it is to circulate hot water, thanks

If you ask the correct question , you will get the correct advice, what you posted was complete twaddle, you have an S plan with 1 circulating pump, and you have a DHW secondary return pump, absolutely not the same thing as you described, you can put the secondary return pump on a seperate timer, or use PIR sensors to turn it on when someone enters the bathroom or whatever