W-plan pump run on

[davidwf]

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

 

[ShaunCorbs]

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

 

[davidwf]

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 !

 

[ShaunCorbs]

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 !

Yes that’s a w plan valve you only have heating once hot water is satisfied

 

[John.g]

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 !

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

 

[davidwf]

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

 

[davidwf]

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

 

[John.g]

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

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)

 

[davidwf]

....and your diagram clearly states A to CH !!!...not as you said earlier.....

 

[John.g]

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

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.

 

[davidwf]

which I believe it is.....will have to get a meter on it to check when it is powered and where it is etc....maybe C and 1 are swapped ???

 

[davidwf]

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

 

[ShaunCorbs]

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

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

 

[davidwf]

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

 

[ShaunCorbs]

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

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

 

[John.g]

Yeah,

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

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/.

 

[davidwf]

dunno.... I will have to check where the cables go and also what is wired to where....what a nightmare 😡
....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

 

[davidwf]

...............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/.

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 ????

 

[davidwf]

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

 

[John.g]

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??

 

[davidwf]

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

 

[John.g]

It should be OK to shut the bypass since the water allways has somewhere to circulate.

 

[ShaunCorbs]

dunno.... I will have to check where the cables go and also what is wired to where....what a nightmare 😡
....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

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

 

[ShaunCorbs]

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

Yes as one port is always open

 

[davidwf]

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

 

[ShaunCorbs]

You sure your drawing is correct 100% as your boiler requires a perm live and a switch live ?

You sure the red wires arnt perm lives ?

 

[John.g]

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

View attachment 94764

That looks correct to me, when you do get there suggest turning both roomstat and cylinderstat to a high setting, when pipe B? to the cylinder coil gets hot about a foot from the diverter valve (and pipe A remains cold, turn roomstat to a low setting (no call) then turn down the cylinderstat, check that pipe A remains cold during boiler overrun.

 

[ShaunCorbs]

Easy way to fix the issue is to get a battery prog room stat eg eph cp4b then move the cylinder satisfied wire and pair it with the prog room stat live and diverter switch eg brown

And then marry up all the switch wires eg boiler switch, pump live, cylinder stat call and prog room stat switch live

 

[davidwf]

ah....apologies for not clarifying... the roomstat we have IS a battery powered one

 

[ShaunCorbs]

ah....apologies for not clarifying... the roomstat we have IS a battery powered one

Easy switch over then just moving some wires etc

 

[davidwf]

....which, surely is the setup I have as in #25 ???

 

[ShaunCorbs]

....which, surely is the setup I have as in #25 ???

No as your drawing there’s no connection between the room stat and the boiler unless you’ve miss labelled the pump as the boiler switch live ?

I suspect you’ve got your perm and switch lives mixed up

Eg yellow going to the boiler perm live to the wirings centre and the red coming from the boiler / pump switch live etc

 

[davidwf]

OK thanks, wont know until I can get over to check.....

 

[davidwf]

OK, so I missed out the fused spur supply...... maybe this is how it SHOULD be......

 

[John.g]

Just a quick look but roomstat & cylinder stats are switching the boiler live , they should be switching a SL on the boiler & the boiler should have a permanet Live to allow it to request/do a pump overrun when both the HW & the room stats are both satisfied?.

 

[Basher]

Not sure this is the exact correct model, but likely similar
Mains from the FCU connects to the boiler at one block.
There is a separate connection block to accommodate a live (out) supply to eg thermostat , a switched live (in) from eg thermostat, a neutral etc etc as below simple example.

Ls is live supply (out). Lr is switched live (control in)

So the Boiler L in the diagram above (post #34 yellow and grey wires) should actually be Lr in the boiler. Hopefully it is like that already.

 

[davidwf]

Again thanks for the prompt replies.....I will check I all out when i next go over ......and will of course report back 😁

 

[davidwf]

right.....having gone through all the connections it appears that on the cylinder stat, C & 1 were reversed....the stat is actually marked 1,2,3 rather that C,1,2 which might explain it
I have corrected this and re-drawn the actual installation as it is, I also fitted a new Drayton home battery operated programmable thermostat just to eliminate that
When I tried it yesterday it all seemed OK but was later advised that after the water had been on the rads were still getting hot at the top - suggesting a short run rather than being on all the time
The diverter valve is new and moves and seals OK

 

[Basher]

As far as I can see, the only difference the reversal of C and 1 would make, is that the diverter valve would be permanently powered once the cylinder stat is satisfied, irrespective of whether timer is on or off.
Having corrected the C/1 swap, the diverter is no longer powered once the timer is off.
So I hope residual boiler heat won't now be continually pumped around the rads as before, but it seems there's still something of that effect?

Well done for finding that wiring feature!

 

[davidwf]

yes....but if the diverter valve IS / WAS being held open that would explain the residual heat around the rads whilst the pump was over-running......it is only a small house with small rads
I will do another check in case I have missed something but, with it operating as it should, there's no way the residual heat CAN circulate around the rads is there.......unless the pump pressure is keeping the valve open but that is unlikely
"feature" indeed 🙄

 

[Basher]

yes....but if the diverter valve IS / WAS being held open that would explain the residual heat around the rads whilst the pump was over-running......it is only a small house with small rads

Yes absolutely!

I will do another check in case I have missed something but, with it operating as it should, there's no way the residual heat CAN circulate around the rads is there.......unless the pump pressure is keeping the valve open but that is unlikely
"feature" indeed 🙄

I don't think you've missed anything! Now the diverter should return to hot water position when the programmer/thermostat are off, so hopefully no spurious heating any longer 🏅.
I was just slightly surprised by the report that rads were still getting hot at the top after water heating, as the diverter surely shouldn't operate if heating isn't called for 🤔

 

[davidwf]

So was I 😅......it is possible that I have mis-wired it again as even I got confused with the C/1/2 and 1/2/3 labelling and have also swapped the colours around to try and simplify (!!!!) things

 

[John.g]

So was I 😅......it is possible that I have mis-wired it again as even I got confused with the C/1/2 and 1/2/3 labelling and have also swapped the colours around to try and simplify (!!!!) things

What is the cylinder stat exact make and model?.

Did you do the basic test of feeling pipe A (should be cold/cool) when HW calling and boiler firing and should remain cold/cool on pump overrun.

 

[davidwf]

not sure of exact make but it had the terminals marked 1-2-3 .... looks identical to this one (attached)
....yes, at least whilst the HW was on the pipe seemed to remain cool
will check again when I can get over there....again 🙄

 

[Basher]

Someone got confused when writing the instructions!🤔🤪

 

[davidwf]

I wondered about that...... but I think the printed version is correct....
so C & 1 are connected when it is calling for heat i.e. when the water temp is lower than the set point
when it is satisfied contacts C & 2 will connect as per my diagrams
...it all depends on what they are calling normal.... in my opinion, normal is whan everything is satisfied co normally open would be C & 1

 

[John.g]

I wondered about that...... but I think the printed version is correct....
so C & 1 are connected when it is calling for heat i.e. when the water temp is lower than the set point

Looks that way to me, so, in the installed stat. 1&2, (where 1 is "C" & 2 is "1") are made when the water temp is < the SP, I would turn up the stat fully and check for continuity between 1&2.

when it is satisfied contacts C & 2 will connect as per my diagrams
...it all depends on what they are calling normal.... in my opinion, normal is whan everything is satisfied co normally open would be C & 1

then turn the stat fully down and check for continuity between 1&3.

Also check that pipe A remains cold on the pump overrun, if so, the only other explaination I can think of is some form of reverse circulation.

 

[davidwf]

Apologies again for the delay in response.......I have been pretty much laid up for 8 weeks with sciatic pain 🙄 but its finally easing.....

I have just re-checked EVERYTHING
The system IS wired as per my latest diagram in post #38
The cylinder stat operates correctly with continuity between C & 1 calling and C & 2 satisfied
The connector block wiring is all correct as per diagram
The diverter valve doesnt seem to be leaking or bleeding to the rads circuit in its' closed / normal position, it ONLY moves when the roomstat is calling for heat and returns to normal position when the roomstat is satisfied
The pipe from the diverter to the rads ONLY gets hot when it should
The pump overruns for approx 5 minutes during which time, with the roomstat satisfied, no heat (correctly) goes through the rads
With the HW satisfied and the roomstat calling, all the heat goes to the rads
With the roomstat calling, if I turn up the HW stat to calling the diverter valve closes and diverts all the heat to the HW
With the roomstat calling, if I turn it down to satisfied the diverter valve closes to its normal position (HW)

So, as far as I can see it is all physically, mechanically and electrically correct and functioning as it should......time, as they say will tell

 

[John.g]

Post #38 shows wire blue to C, brown to 1 and black to 2 (on the stat) but your stat is numbered 1,2&3? so what colour wires go to these numbers?.

 

[davidwf]

not sure why they have labelled it as normally closed.....it is closed whilst calling for heat, exactly as shown

 

[Basher]

not sure why they have labelled it as normally closed.....it is closed whilst calling for heat, exactly as shown

That is standard nomenclature. The contacts "normally closed" are connected when the thermostat is not doing anything, i.e. not hot.
When heat is applied, i.e. the system is activated to produce heat until the set point is reached, then the contacts will eventually open and the heating stops.
If you called them 'normally open', and you connected those contacts to the heating, nothing would happen!

Same with a relay. "Normally closed" means the unactivated state.
I was just brought up with this convention in electronics, and don't understand the issue!

 

[davidwf]

surely "normally" equates to satisfied - i.e. the water HAS heated up and no further action is needed....so in its' normal state it is satisfied .....the connections and make / break indications are correct, just the nomenclature is confusing
in a roomstat the contacts are normally (i.e. satisfied) open, closing when heat is required
we could probably argue and counter argue this until the cows come home.....😁

 

[davidwf]

the only other thing I can think of - but dont understand why - is that the 15mm bypass gate valve around the pump was open about 2 turns
As the system has no TRV's I have fully closed this now.....could it have possibly affected anything ?
I understand WHY it is provided on a system with TRV's but not in this installation........this is a W-plan system remember so surely as the diverter will be either HW or CH (or, if it ever gets stuck, somewhere in between as was the original issue) and with no TRV's fitted to any rads there is no need for a bypass valve / loop as the water will always have somewhere to circulate

 

[John.g]

This is similar to your one, I think the description might be less confusing if it just left out the "Normally" and describe it like on the EPH pipe/cylinder stat.

 

[John.g]

the only other thing I can think of - but dont understand why - is that the 15mm bypass gate valve around the pump was open about 2 turns
As the system has no TRV's I have fully closed this now.....could it have possibly affected anything ?
I understand WHY it is provided on a system with TRV's but not in this installation........this is a W-plan system remember so surely as the diverter will be either HW or CH (or, if it ever gets stuck, somewhere in between as was the original issue) and with no TRV's fitted to any rads there is no need for a bypass valve / loop as the water will always have somewhere to circulate

One could understand if the bypass was between the boiler flow and return because (on a Y plan anyway) a separate 2 port Motorized valve is supposed to be installed additionally on the cylinder coil because it fails shut whereas a MPV or Diverter valve will fail open to the cylinder.

 

[davidwf]

This is similar to your one, I think the description might be less confusing if it just left out the "Normally" and describe it like on the EPH pipe/cylinder stat.






View attachment 95025

thanks....
yes, so my diagram and wording is correct....c +1 calling, c+2 satisfied..... maybe just that wording would be simpler

 

[davidwf]

Well I dont know........having previously tested and fully confirmed correct operation I was confident it would be OK.....which it seems it has been for a while but yesterday I got "the call"........and sure enough the rads are getting hot when the HW is running and the wallstat is off 🤬 ...I have also replaced the wall stat for good measure.
The motorised valve appears to be operating as it should - I haven't removed the cover but the indicator lever seems to be moving correctly but the CH pipe is definitely getting hot.
Wondering now if it's worth doing it properly and converting to fully pumped Y plan .......I THINK it will only need re-wiring (and of course a new 3 way valve) and I would fit a programmer at the same time ..
the only thing I can think of is that the valve is sticking or is not sealing due to debris but the original water was clean and I drained and refilled it adding Fernox anyway..
..
....any better suggestions ?

 

[John.g]

Well I dont know........having previously tested and fully confirmed correct operation I was confident it would be OK.....which it seems it has been for a while but yesterday I got "the call"........and sure enough the rads are getting hot when the HW is running and the wallstat is off 🤬 ...I have also replaced the wall stat for good measure.
The motorised valve appears to be operating as it should - I haven't removed the cover but the indicator lever seems to be moving correctly but the CH pipe is definitely getting hot.
Wondering now if it's worth doing it properly and converting to fully pumped Y plan .......I THINK it will only need re-wiring (and of course a new 3 way valve) and I would fit a programmer at the same time ..
the only thing I can think of is that the valve is sticking or is not sealing due to debris but the original water was clean and I drained and refilled it adding Fernox anyway..
..
....any better suggestions ?

On HW only, actuator unpowered, you should feel a fairly stiff resistance immediately on pulling on the manual lever, if you do and IF the actuator is attached to the valve spindle then the valve must be positioned correctly to port B (HW), so either the valve is passing or there is some form of reverse circulation, you could just remove the actuator and ensure the valve manually to port B only.
You say "the CH pipe is definitely getting hot.", I would expect the CH pipe to get hot due to conduction (if copper) for a maybe a foot or so but wouldn't expect even the rad tops to become hot.
You might try and see where the cyliner coil returns to the boiler and its position in relation to the rad returns.

 

[davidwf]

Thanks but no, the pipe is getting HOT....... bloody hot....its more than simple conduction along the pipe

 

[davidwf]

IF I do decide to change it to Y plan are there any recommendations or avoids regarding makes.....would like to avoid the cost of the Honeywell one if possible but clearly don't want to be replacing it again next year because I bought a cheap one.

 

[ShaunCorbs]

S plan it eph

 

[davidwf]

Too much re-work....its only a small 2 bed house and the y plan would be so much simpler to install

 

[John.g]

Look up MOMO mid position valve, these apparently are only powered while changing position or modify a normal MPV, it will then allways return to the unpowerd state, only requires a extra relay.

 

[davidwf]

thanks.... that looks interesting rather than having the motor in a stalkled position 99% of the time.....they seem to be quite rare though
Can anybody recommend / avoid a "normal" spring return one ...

 

[John.g]

thanks.... that looks interesting rather than having the motor in a stalkled position 99% of the time.....they seem to be quite rare though
Can anybody recommend / avoid a "normal" spring return one ...

You can see if you read through the attached Link that the MOMO actuator contains far more circuitry than the conventional MPV, I definitely know that the modified MPV above, (I actually got that nice schematic from the attached Link), certainly seems to extend the MPV lifespan as a very old electrical friend of mine did this very mod years ago, he has since passed on but the MPV is still there and must be ~ 15 years old now. You have a electrical background? so should have no problem in implementing it. Some, mistakenly think that just programming on the HW last thing at night for a few minutes is enough to power down the MPV and it will, but only if the cylinder stat is also, very unlikely, calling, there should be at least a 6/7 hour powerd off state alone each night with the mod since CH is normally the last port of call at night.

Motorised Valves - DIYWiki

wiki.diyfaq.org.uk

 

[davidwf]

thanks but......for simplicity I think I would prefer to go with a conventional 3 port spring return motorised one
Which to avoid though ????

 

[John.g]

thanks but......for simplicity I think I would prefer to go with a conventional 3 port spring return motorised one
Which to avoid though ????

Honeywell, I believe, were the go to product at one time but maybe not so much now, I hear good reports of EPH though.

 

[exedon2]

We use eph stuff all the time very reliable but I still wouldn't fit a 3 port valve.
Your draining down and saving £30 against two 2 ports ain't worth doing .
Y plan = shorter lifespan and more difficult to trouble shoot.

 

[davidwf]

OK, I get the idea (and potential benefit) of S plan and I would be quite capable of plumbing it myself....but....the boiler has an overrun that pumps for around 4 mins.....I already have a manual bypass valve (which is closed as there are NO TRV's in the system) but the bypas loop is literally a 15mm bypass around the pump so surely there will be insufficient "loss" in the simple pipework to dissipate the heat?
As it is, the overrun will pump around the HW circuit
and.... 2 x zone valves are considerably dearer than an EPH mid/3 position one which I can get for £65

 

[davidwf]

any thoughts regarding the bypass loop ?

 

[davidwf]

If I convert to Y plan do I need a mid position or 3 port valve.... I THOUGHT they were one and the same....they both have 3 ports!

 

[John.g]

You can get a (3 port) diverter valve that will give you CH or HW, you can also get a (3 port) mid position valve to give CH only, HW only, and CH&HW, thats why its called a mid position valve.

 

[davidwf]

hmmm...so, If I were to convert to Y plan presumably I need a mid position valve for my installation?

 

[John.g]

Convert from what?, a S plan which has separate 2 port valves for CH & HW or a W plan which has a 3 port Diverter valve as above but only gives CH or HW.

 

[davidwf]

convert from the existing W plan...
If I changed it to S plan, when both are satisfied there would be nowhere for the residual heat to circulate ....as mentioned, the bypass loop appears to be just that - a 15mm pipe around the pump which I am not sure IS a bypass loop as such
"only" CH or HW is fine as it is quite a small house and the HW requirement is low

 

[John.g]

convert from the existing W plan...
If I changed it to S plan, when both are satisfied there would be nowhere for the residual heat to circulate ....as mentioned, the bypass loop appears to be just that - a 15mm pipe around the pump which I am not sure IS a bypass loop as such
"only" CH or HW is fine as it is quite a small house and the HW requirement is low

You could go the conventionel way of installing a ABV between the boiler flow&return if converting to a S plan otherwise convert to a W system with a 3 port diverter valve.

 

[davidwf]

possibly..... just possibly.......
I suggested he turned the CH stat right down and turned the HW stat right up......popped over to the house this morning and found the rads were red hot.
Investigation found that the valve was not returning fully to the home position when the CH satisfied (W-plan remember)……there was no voltage across the motor so nothing could be holding it open
I undid the 2 screws that hold the backplate to the brass valve about 1/2 a turn and the assembly immediately fully opened which should of course close the CH circuit…….did them back up and operated it again and it was quite stiff and didnt return fully…..
I have put two small washers between the backplate and the brass valve to space it out a little bit and it now APPEARS to be working properly !.....hmmm
...and that was a brand new unused Honeywell V4044C1288/U 22mm 3 Port motorised diverter valve, sadly bought off a private seller on ebay so no guarantee, the backplate looks straight and there are no dents or anything anywhere

If it continues to work OK I will take that as a win 😀

 

[davidwf]

You could go the conventionel way of installing a ABV between the boiler flow&return if converting to a S plan otherwise convert to a W system with a 3 port diverter valve.

it already IS (and always has been) a W-plan system with motorised diverter valve..........

 

[davidwf]

pleased to report that it is still functioning correctly as per my findings......so much for buying expensive Honeywell !