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W-plan pump run on

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davidwf

davidwf

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Son recently moved into a 20 year old house with what appears to be a W-plan system using, I think a Worcester Bosch Greenstar gas boiler
He noticed that the rads were getting hot when the HW was on and I diagnosed the 2 position diverter valve (not 3 position valve!) was well and truly seized in the open position.
Having replaced tis expensive (£150) item HW now gets hot and the rads dont......until the cylinder thermostat temp is reached and the valve moves to the CH position which all seems correct.....but the pump continues to run for several minutes as I believe it should during which time it is now pumping the residual heat around the rads !
Cant see any way around that apart from changing to a mid position valve and Y-plan which, having just fitted a new one I dont really want to do as it may well involve additional wiring as well as wasted ££££
Is that simply a disadvantage of the W-plan system that we have to live with ???? seems rather daft if it is
 
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It’s pump overrun as the boiler has an alu heat exchanger you could alter the wiring but this would invalidate any warranty with the boiler
 
Yes, I realise WHY it is running.....but as I said is it a "feature" that, once the HW is satisfied the residual overrun heat will divert to the rads ?....seems a bit daft .... especially in summer !
 
davidwf said:
Yes, I realise WHY it is running.....but as I said is it a "feature" that, once the HW is satisfied the residual overrun heat will divert to the rads ?....seems a bit daft .... especially in summer !
Click to expand...

Yes that’s a w plan valve you only have heating once hot water is satisfied
 
davidwf said:
Yes, I realise WHY it is running.....but as I said is it a "feature" that, once the HW is satisfied the residual overrun heat will divert to the rads ?....seems a bit daft .... especially in summer !
Click to expand...
On a diverter valve, (W plan) port A goes to the HW, port B to CH, on a MPV port B is HW, port A is CH, is your son's diverter valve plumbed in or wired correctly I wonder, reading this the diverter valve will only go to port B if the CH is calling and the HW is satisfied?. So on pump overrun what makes the valve change over to CH for the overrun period?.

W Plan central heating system

W-plan central heating system operation and wiring diagram
flameport.com flameport.com
 
Boiler is Greenstar 30 CDi conventional and was replaced around 8 years ago....to my mind it is way too big for the small 2 bedroom house it is in

Pretty sure the valve is correct.....at least we reaplaced it "as was" .... will check later
The valve seems to be in the home position - i.e. un-operated - when HW is demanded and moves once the thermostat has switchd to the satisfied position which seems correct.....but when it has done so and the pump overrun is still operational surely the only flow CAN be to the rads for the duration of the overrun
Wiring is messy - clearly done by a professional 🤣🤣 the black cable is to the diverter valve, the white one (3 core & earth) to the cylinder stat....there is no programmer so the HW runs all the time and the CH is via a time-programmable electronic wall stat - that seems to be working OK
The pump wiring disappears towards the boiler - i.e. it isnt connected to this block
 

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davidwf said:
Pretty sure the valve is correct.....at least we reaplaced it "as was" .... will check later
The valve seems to be in the home position - i.e. un-operated - when HW is demanded and moves once the thermostat has switchd to the satisfied position which seems correct.....but when it has done so and the pump overrun is still operational surely the only flow CAN be to the rads for the duration of the overrun
Click to expand...
Not sure why you say the flow can only be to the rads during overrun, the cylinder will still act as a heat sink for the boiler heat exchanger when water is circulating through it?
The schematic below is probably basically much like yours, ie HW priority, if CH is also selected and calling then the valve wont change over (to rads) until the cylinder stat is satisfied, its contact 2 will then supply 230V from the roomstat to open the valve to CH, if CH satisfied or switched off while the cylinder stat is still satisfied (which it will have to be, otherwise the HW will take priority again), the 230V to c/o the valve is allways supplied via roomstat "call" contact 2 then to cylstat contact "C" and cylstat satisfied contact 2, so once the cylinderstat is satisfied or switched off then the valve is unpowered and returns to the HW mode (even on onerrun)

1722173639104.png
 
davidwf said:
john.g:
according to the instruction sheet A goes to CH and B to HW......which is the way it is installed.....extract attached

View attachment 94742
Click to expand...
Yes, I read it from other source as A to HW (W plan) and B to CH, but definitely, its B to HW on a MPV and A to CH so one would imagine the diverter valve to be the same, one way or the other, when unpowerded the open port should/must be to HW.
 
deffo A to rads.....ah well, at least I wont have to drain down again.....
so..to recap... the valve should never be powered and always be in the home position when HW only - i.e. as now, in summer
 

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John.g said:
On a diverter valve, (W plan) port A goes to the HW, port B to CH, on a MPV port B is HW, port A is CH, is your son's diverter valve plumbed in or wired correctly I wonder, reading this the diverter valve will only go to port B if the CH is calling and the HW is satisfied?. So on pump overrun what makes the valve change over to CH for the overrun period?.

W Plan central heating system

W-plan central heating system operation and wiring diagram
flameport.com flameport.com
Click to expand...

how do you turn the heating on via a room stat as you’ve said you’ve got no programmer ?

So once finished heating the cylinder the power should go via the cylinder stat satisfied term to the prog room stat

Wiring Correct as there’s not enough wires there tbh so my guess is prog room stat goes to the boiler only

And cylinder stat wiring looks missing a core eg com,heat, satisfied and earth
 
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ShaunCorbs:
as mentioned in#6....... the wall stat is a programmable timer type ....in effect the "programmer" terminal is always on, the programs in the roomstat call for heat as required
 
davidwf said:
ShaunCorbs:
as mentioned in#6....... the wall stat is a programmable timer type ....in effect the "programmer" terminal is always on, the programs in the roomstat call for heat as required
Click to expand...

But does that go to the heating wiring centre as they used to do it wired to the boiler pump only as you’ve had yours changed will need adjusting

Also updated the above post
 
Yeah,
davidwf said:
deffo A to rads.....ah well, at least I wont have to drain down again.....
so..to recap... the valve should never be powered and always be in the home position when HW only - i.e. as now, in summer
Click to expand...
Yeah, Flameport are normally fairly accurate in their descriptions but obviously not here.

The other interesting point is that in my diagram above (and I think, yours) is that even if the HW was timed (or switched off) then with CH selected and calling the cylinder will still heat up first if the cylinder stat is calling, the valve will then c/o when the cylinder stat is satisfied/.
 
dunno.... I will have to check where the cables go and also what is wired to where....what a nightmare :mad:
....but even if the roomstat goes to the boiler (which I am prtetty sure it doesnt) , as it is not calling for heat it shouldnt matter
 
John.g said:
...............The other interesting point is that in my diagram above (and I think, yours) is that even if the HW was timed (or switched off) then with CH selected and calling the cylinder will still heat up first if the cylinder stat is calling, the valve will then c/o when the cylinder stat is satisfied/.
Click to expand...
indeed..but only IF the roomstat was calling for heat which of course it isnt......unless the relay contacts are welded or stuck....
hmmm.... multi-meter and more delving clearly required

so how the hell are the rads getting hot ????
 
I have NOT traced these out yet but if we assume them to go where I think they go (attached) then the wiring appears to be correct...the roomstat doesnt need a N connection
my diagram.jpg
 
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So, the rads are only heating up when the HW is satisfied and the pump is on overrun?, if so, then seems the diverter valve is changing over to CH. You wouldnt imagine them getting too hot with the burner off. Are you sure theres not some reverse flow through them when the boiler is firing on HW??
 
not sure, no.......report was "the tops are getting hot" so one would assume they arent ring supplied all the time the HW is running or else they would be very hot all over

One other question.... around the diverter pipework is a 15mm bypass....as he doesnt have any TRV's can I close this off?... it is about 2 turns open at the moment
 
davidwf said:
dunno.... I will have to check where the cables go and also what is wired to where....what a nightmare :mad:
....but even if the roomstat goes to the boiler (which I am prtetty sure it doesnt) , as it is not calling for heat it shouldnt matter
Click to expand...

No but the valve for heating to open eg heating on is fed from the cylinder stat satisfied so every time the cylinder is satisfied the valve opens for heating

When in reality it would send power to the prog room stat and then the valve etc
 
davidwf said:
not sure, no.......report was "the tops are getting hot" so one would assume they arent ring supplied all the time the HW is running or else they would be very hot all over

One other question.... around the diverter pipework is a 15mm bypass....as he doesnt have any TRV's can I close this off?... it is about 2 turns open at the moment
Click to expand...

Yes as one port is always open
 
I THINK I have re-drawn it correctly "as-is".....without programmer connections etc.

IF correct I agree there's no way the diverter can be operating....
how about IF any of the cyl stat connections are reversed.....
appreciate thats a lot of IF's but I havent been able to get over there yet

diagram.jpg
 
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