Adding underfloor heating to a s-plan system

[Delboybully]

I am doing the electrics for an extension, part of which is to add a wet underfloor heating system.

The current heating is s-plan, the boiler has a pump overrun.

The plumber has put in a 2port valve and pump which feeds one zone on the UFH with a remote programmable theromstat.

The difficulty I am having is getting the boiler to fire when the UFH calls for heat without sending power to the existing pump (this is from dagrams, its not wired yet). The boiler has L and N, the call for the boiler to fire going into the boiler and the existing pump power is from the boiler.

Anyone any ideas?

 

[Leesparkykent]

A relay. Edit: why don't you want the existing pump to run?​

 

[Delboybully]

Its not me its because the plumber didnt want to run his pipes into the existing cupboard the lazy b.

Gonna have a think about using a relay and will get back, probably with another question

 

[Delboybully]

I dont want the existing pump the run when the underfloor heating is on, because there will be times when the Ch and HW is off. Then the pump is pumping with nowhere to go. Ive not done much on CH systems- i think it called the boiler interlock

 

[dansk]

you need two relays for the boiler enable, then the new UFH & pump can be on the S/L from the UFH stat and do the same for the CH & HW, this way there wont be any back feed.

To better explain: 2 relays are used to activate the boiler. On relay 1 wire the Oranges from the H/W & CH (including the pump) to A1 and do the same with relay 2 putting the new UFH valve orange and pump on to A1 - this will keep them split.

 

[Delboybully]

This makes sense, a couple of contactors. So when the existing system calls for boiler on, only the existing pump comes on, when the UFH calls for heat, its pump comes on.

Makes sense now, thanks

No thanks button on the screen or I would thanks you both!

 

[Leesparkykent]

You want both pumps to run when under floor heating calls for heat but only the original pump to over run when underfloor heating valve shuts off?

 

[Leesparkykent]

This makes sense, a couple of contactors. So when the existing system calls for boiler on, only the existing pump comes on, when the UFH calls for heat, its pump comes on.

Makes sense now, thanks

How would the pump run on as the boiler has pump over run?

 

[dansk]

I was thinking the same, but whats the point of pump overun if the valves are closed?

 

[davesparks]

you need two relays for the boiler enable, then the new UFH & pump can be on the S/L from the UFH stat and do the same for the CH & HW, this way there wont be any back feed.

To better explain: 2 relays are used to activate the boiler. On relay 1 wire the Oranges from the H/W & CH (including the pump) to A1 and do the same with relay 2 putting the new UFH valve orange and pump on to A1 - this will keep them split.

That'll kill the boiler in a few months, hope his insurance is up to date!

Overrun boilers must have a pump connected to the pump overrun terminal.

 

[Leesparkykent]

I was thinking the same, but whats the point of pump overun if the valves are closed?

Because the boiler has to dissipate the heat other wise it will kill the heat exchanger. There should be an automatic bypass so the pump can still pump round the flow and return when the valves are closed.

 

[dansk]

Yes agreed about the pump o/r - but i suspect if thats the case in this set up, im wonder if the op has all the facts.

 

[dansk]

problem solved -

 

[Leesparkykent]

Like this but the original pump will be connected to the pump live terminal in boiler, oranges connected to switch live in boiler and boiler permanent live connected with the greys of the valves.

 

[davesparks]

It's very unusual to run the underfloor pump without the circulating pump, but then I haven't seen the pipework to know what's going on.
To achieve seperate pumps will require two relays connected so that they each connected run their respective pumps when the call signal is live from the valves but also the normal circulating pump must default to being connected to the boiler pump terminal.

The normal setup is that the underfloor pump only circulates water through the underfloor heating after the blending valve, with the normal circulating pump effectively delivering the hot water to the underfloor system. To do this you can use just one relay to operate the boiler fire from the underfloor valve