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meerkat

potterton, s plan, system fault

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meerkat

Hi, fault on a Potterton S plan sytem,

the HW and CH circuits are both on continually,

I havent actually seen the job yet,

my thoughts are:

one or both motorised valves stuck open,

or wiring fault between room stat and CH valve

and or wiring fault between Cylinder Stat and HW Valve,

or incorrect wiring of live feed to both Valves

any help greatly appreciated, cheers (MEERKAT)

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Doc Hudson

I think you need to fully establish the symptoms first. Do they mean HW & CH are continually on all the time even when both are switched off, Or do they mean both come on when either is switched on, Does either either circuit work correctly at any stage or is everything always faulty. Have they had any recent alterations, plumbers or other? Could be incorrect wiring giving wrong signals out to the valves or a back voltage holding a valve driven from the switch on the other valve. Its unlikely two valves have both failed? I think you need to go and disconnect a few parts to test one half on its own then add the the other half back in. Keep a pen and paper handy to note the cable types & colours used. and assume it has never worked correctly so double check every wire connection and don't take anything for granted. Only trust the items you have tested yourself, take it a step at a time and don't assume! Good luck with it Meerkat, let us know how you get on.

Doc H.

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Theorysparky

print this

Honeywell Wiring Guide & Fault Finding on Central - Downloads - Talk.electricianforum.co.uk... a forum with a difference.

a4 pad and pen required

questions to ask

how long has it been like it

have you had any work done

did you do anything that may have caused this ie storing cases etc in the airing cupboard (common one)

i would also take a decent wiring centre with you just incase its a choc block patress affair...

also check the lights on the programmer dim lights will indicate a faulty one.........

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meerkat

thanks Doc, and theory, logical approach to the diagnoses is,

customer has a leak at the boiler calls out a plumber,

plumber replaces a potterton boiler, with a Baxi boiler,

he also replaces the PCB, I presume he must have damaged it or it just gave up the ghost,

plumber leaves, a few months later the the elderly lady notices that the CH and the HW seem to be permanently on

even if room stat is not calling for heat, customer is turning the boiler off and on to regulate the heating and hot water.

I dont know what the plumber has done regarding connection or disconnection of any wiring.

Customer calls out a heating engineer, he say's that a motorised valve isnt working correctly and he say's his electrician friend would come round and sort it,

well no one has turned up.

I said I would have a little look to see if it was anything obvious,

I have installed a combi boiler in my own home and understand the basics of a heating system,

however this system had a Baxi boiler down stairs feeding what looked like a heat store type vessel in the airing cupboard,

the pipework has 2 motorised valves, and 2 pumps, which I guess is a closed S Plan setup,

on removing the faceplate of the heatstore vessel I came across the PCB and all its connections,

all the cables have been labelled and everything appeared to be ok,

I haven't done any testing yet, my thoughts were to ensure that the wiring at the PCB and ancillaries is all connected correctly, then to set the room STAT to call for heat, then to set the tank STAT to call for heat and see what happens,

if the wiring is ok, could the fault be due to a stuck open valve?

and if so, how difficult is it to replace, I guess the system would have to drained first, then replace faulty valve and refill

sorry this is long winded, thanks for any help much appreciated (MEERKAT)

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sellers

ok after that, my theory is as follows, faulty valve isn't working properly, as a temp valve has been manually opened or is stuck open, and wiring may have been altered to allow the boiler to function properly (as best it can). I'd guess at he CH valve, or wiring related to it.

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m4tty

I think some motorized valves can be changed without draining the system. May be wrong tho so stand to be corrected

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meerkat
I think some motorized valves can be changed without draining the system. May be wrong tho so stand to be corrected

cheers Matty, sombody did mention that was possible, but if the problem was with the motor or microswitch then it would destroy the replaced items anyway, so best to change valve completely, thanks anyway (MEERKAT)

---------- Post Auto-Merged at 19:20 ---------- Previous post was made at 19:18 ----------

ok after that, my theory is as follows, faulty valve isn't working properly, as a temp valve has been manually opened or is stuck open, and wiring may have been altered to allow the boiler to function properly (as best it can). I'd guess at he CH valve, or wiring related to it.

thanks for that Sellers,

how easy is it to drain, replace and refill a system like that and are there any pointers to watch out for, cheers (MEERKAT)

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sellers

not sure meerkat, I stay away from the plumbing side!

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NozSpark

Should be pretty easy to see if it's the valve head or body... Especially if it's honeywell valves as the disasemble really easily, two screws to remove the head

Then you'll see the stub sticking out of the valve body,, if that's stiff then the body's had it,, otherwise you can see if the motors turning by giving it a demand signal and see if it turns...

If it does have honeywell components then get the honeywell literature that theory linked to

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Theorysparky

^+1

the heads are not to expensive and are generic

i would check the wiring out first 10 min job

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chrishaworth

99.9% chance the plumber has got the wiring wrong. Different boilers have different terminals for LNE, switched live, room stat, cylinder stat etc. It's quite likely that he noted down the terminal number that each wire went to on the old boiler and connected them to the same terminals on the new boiler. You'll need the boiler manual and a bit of tracing to get the right terminals. Valve bodies do occasionally stick, but to have 2 doing it at the same time is stretching coincidence. Anyway, even if both valves were stuck open, the boiler still should not fire if the programmer is not calling for heat or hot water as there should be no supply to the grey wires on the valves. Patience and persistence are required. (The third P is if you can't fix it, get pi**ed).

Cheers. Chris

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SPECIAL LOCATION

Other points for your consideration Meerkat....

Some less "quality" brands of valves have plastic housings....

these have small lugs that the valve return springs hook around...

I have know these small lugs to break off..

so the spring to manually pull the valve back to the "closed" position Doesn't!!

This can mean..

A) the valve is always open so when the other valve is on some water also flows through the jammed open valve!

B) the valve AND the micro switch are jammed on so it is always calling for heat and let's hot water go down that part of the circuit!

GuinnessGuinness

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meerkat

thanks Noz, Theory, Chris and Special, some very good advice,

I plan to check wiring especially at the boiler (referencing the manual)

I will then check out the programmer and both stats and then move on to valves if all is well,

thank you all for the input, I appreciate your help (MEERKAT)

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Doc Hudson

I thought you had been and were reporting back your findings then Meerkat, we shall all have to wait a bit longer!

Doc H.

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