Switching

[Mark.W]

Evening Chaps

I've got a switching conundrum that I was hoping one of you guys could help me with!

I've been working on a heating system and the previous spark managed to run 2 pumps either together or independently with one boiler and a 2 channel programmer!

I however cannot get pump 1 to run without pump 2 also running, because they have a common live at the boiler??
I've tried everything and had to resort to using a NC contactor to stop pump 1 from running when pump 2 was running, but the previous spark never used a contactor.

I hope that made sense, if you need any further info just give me a shout!

Thanks for your help!
Mark

 

[SYKRAPS]

Hi Mark,

What type of heating system is it and what is the job that each of the pumps are carrying out within the heating system?

 

[Mark.W]

Hi

It isn't any type of system, basically all there was, was 2 pumps and no valves. 1 of the pumps controlled upstairs heating and the hot water and the other pump controlled downstairs heating. There was one room stat on downstairs pump and that was it no stat for upstairs heating and also no cylinder stat, the cylinder stat apparently got taken out recently when the customer had solar thermal installed!

Very bad I know!!

 

[SYKRAPS]

Was it an old style hortsman twin chanel timer or a newer digital one?

 

[Mark.W]

I think it was a newer one, it looks very similar to the lifestyle programmer!

 

[bigspark17]

isit an old system.? sounds like the downstairs pump should be wired off the roomstat hest rise terminal.! but what is controlling HW and up rads.? not just the programmer i hope, if no cyl stat whats stopping cyl acting like a big kettle.? hope its a vented cyl.?

 

[Mark.W]

We've just turned upstairs circuit into an S plan by putting valves in for HW and HTG! Left downstairs as it was, on its own pump and controlled via the room stat! We've also installed a new upstairs room stat and cylinder stat, which yes as you thought, was fed directly from the programmer!

 

[bigspark17]

sounds like you done a good and very needed upgrade to this system.! if you wire your pumps from the motorised valve rather than from the boiler you can eliminate the shared pump live at the boiler.!

 

[SYKRAPS]

Well it sounds to me like an old gravity hot water system with pumped central heating and as an effort at controlling it they have bodged it up a bit. The only way that I can see it would have worked is that the prog was configured as a time switch where you can have the HW side on independantly but the CH side would only work if the HW was calling.

Wired from the HW side of the prog would be the upstairs pump for CH and the HW circuit and the boiler.

Wired from the CH side of the prog would be the downstairs pump for the CH and nothing else, so you could not have the downstairs CH on unless the upstairs CH and the HW is calling at the clock.

This is the only way that I can think of to have the pumps working independantly.

Very old school.

 

[SYKRAPS]

sounds like you done a good and very needed upgrade to this system.! if you wire your pumps from the motorised valve rather than from the boiler you can eliminate the shared pump live at the boiler.!

Both pumps will be common with the boiler switch live so they will both work which ever is calling, got to be careful that you don't have a pump trying to push water up 2 closed valves on the new s-plan part

 

[bigspark17]

aslong as the pumps are wired into calling terminal of the valves (brown + grey) then pumps will only run when being called for.. no need to wire to boiler!

 

[Mark.W]

That's the problem and to counteract that I have installed a NC contactor between P1 and the boiler so that when pump 2 runs pump one is disconnected, the coil is energised by the room stat calling for heat! But how did the previous spark manage to run both pump independently?? That's what has got me baffled! They were both run to the boiler....???

 

[Mark.W]

It worked that when they pressed central heating advance pump 2 would run and when they pressed hot water advance pump 1 would run. Both wired back to the boiler.... Strange!!!!

 

[i=p/u]

What happens when need both pumps running , one after other... I used relay in similar situation before. But running pump from valve seems good

 

[SYKRAPS]

It worked that when they pressed central heating advance pump 2 would run and when they pressed hot water advance pump 1 would run. Both wired back to the boiler.... Strange!!!!

It seems that the HW and boiler worked on gravity and the prog just controlled the pumps in essence and that HW advance controlled pump 1, gravity HW and boiler.