Central Heating Proble, pump running when all controls off, help please

[rowesm]

Background info: Potterton Suprima 80 boiler 5 yr old Honeywell Timer St6400 Honeywell 3 way valve V 4073A 1039 Pump> Grunfos Selectric UPS 15-50 wired to Y plan normal operation allows separate H/water from Heating or both together all rads have thermostats

Problem: Central Heating and water both switched off at timer yet yesterday evening the pump was running and continued to run until we slightly turn the white control anti-clock on the side of the Grunfos pump, the pump then stops running. Switch the Honeywell timer to hot water the boiler lights up but the pump does NOT operate until we turn the white control back slightly clockwise to the 90* setting mark on the pump. So is this another 3 way valve issue or the pump not receiving the correct signal ?

Any ideas or suggestion most welcome, some years ago we were able to replace the 3 way valve after good advice from Roger Mills.

Happy to provide more info if required. Steve

[The Natural Philosopher]

That is almost certainly a stuck 3 way switch.

The heating timers and thermostats control the motorised valve, and the valve itself controls the pump.

See if the valve is moveable by hand, if it is, and this fixes the problem temporarily, the motor may have burned out. If its seized, you will need to dismantle it and try and free it by turning the thing with a wrench. Sometimes crud gets in and jams them but you can free them.

In extreme cases its a drain down or isolate, and a new valve..

[rowesm]

Thanks for your swift response, just some other info, we put the hot water on this morning for 1hr on the Timer, then reset the white control on the Grunfos pump and when the cycle of 1hr finished we had hot water and the pump has stopped runningie back to 'normal' function We don't want to buy one around =A360.00 if this is not the mosyt likely fault.

Does this still sound like a sticking 3 way valve?,

[Heliotrope Smith]

Could be a sticky 3 port. Switch off mains going to boiler and check the manual arm on the valve head, if you can push it side to side with no resistance then the valve is jammed. If however there is a strong resistance and the arm returns automatically when released then the valve is probably ok.

The symptoms you describe suggest to me that the pump overrun is faulty and not switching off in which case a new control board would seem to be the only cure.

The white control on the pump is in fact the pump speed selector and it is not a good idea to switch off the pump by setting between speeds as this would allow the boiler to fire up with no circulation and can cause damage to the boiler.

[rowesm]

Ok here 's the very latest _ the pump stayed back on after the mid day hot water cycle had finished, so I took the cover off the 3 way valve and found the earth wire was off inside the 4073A unit , re-attached the earth wire switched off the circuit tested the value operation as you suggested and found: the 4073A 3 way valve lever was in the central position ie the middle, when I pushed against it to the right there is resistance and then the lever returned to the centre position [presumably on the return springs inside the unit] Does this suggest the valve itself is OK and its just the Honeywell

4073A unit with a malfunction ( this one has been on since 2005). Hope this piece of info helps with the issue at hand.

PS thanks for the info on the pump itself the speed control seems to be variable , we just turned it off last night. I would not leave the cent heating on with the pump speed turned down/ off

[Roger Mills]

This is unlikely to be a 3-way valve problem - otherwise the boiler would fire in addition to the pump running.

You need to check how the pump is wired. Chances are that it is controlled by the boiler - being connected to the boiler's 'pump' terminals. This allows the boiler to 'over-run' the pump after it stops firing in order to carry away the residual heat.

My money is on a duff boiler PCB which is telling the pump to run long after everything has cooled down. This could possibly be intermittent - so it may happen on some occasions but not always.

[Heliotrope Smith]

Ok here 's the very latest _ the pump stayed back on after the mid day hot water cycle had finished, so I took the cover off the 3 way valve and found the earth wire was off inside the 4073A unit , re-attached the earth wire switched off the circuit tested the value operation as you suggested and found: the 4073A 3 way valve lever was in the central position ie the middle, when I pushed against it to the right there is resistance and then the lever returned to the centre position [presumably on the return springs inside the unit] Does this suggest the valve itself is OK and its just the Honeywell

4073A unit with a malfunction ( this one has been on since 2005). Hope this piece of info helps with the issue at hand.

PS thanks for the info on the pump itself the speed control seems to be variable , we just turned it off last night. I would not leave the cent heating on with the pump speed turned down/ off

Seems the 3 port is ok then.

The suprima will operate in pump overrun for a few minutes after burner shut down. Give it at least 15 mins and if the pump is still running then check for 230V on the SWL terminal on the boiler, you should not expect any voltage if there is no call for heat from the controls.

If there is no voltage then it is the pump overrun playing up.

[Mike]

Roger,After undertaking some tests runs with the heat and hot water on then off . I just noticed the pump has stopped after about 20 mins as Heliotrope Smith suggested and the 3 way valve lever is in Auto position with resistance , so can I take it that this points to the PCB rather than the 3 way valve, sorry about this latest update but just finshed our tea and went to check - no noise from the pump !

Pse ignore my reply to you as 'an author' my fault

[The Medway Handyman]

Geoff has asked me to post this for him - guess he has PC problems;

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To the central heating problem pump running ...

I don't seem to be able to post to newsgroups ATM - I get error 441, whatever that is

The Suprima pump overrun is 20 minutes, unless the pcb goes into lockout, in which case, the pump remains permanently powered

Its important to measure whether there is a switched live to the pcb or not. The Suprima pcb doesn't know whether its heating for the DHW or CH.

If the pump is running without a switched live, it has to be the pcb, unless the pump hasn't been wired in correctly

-- geoff

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[Roger Mills]

. . except during the 20 minute period after firing, when it's *supposed* to over-run.

But, in this particular case, it sounds as if it's running for much longer than this - so it's almost certainly the PCB.

[geoff]

In message , Roger Mills writes

Yeah - I couldn't really contribute much, as I've not been able to post most of the day

my website

might be worth a read to the OP

[Mike]

Many thanks to all those who replied , I plan to check the wiring later today, will then update forum

[Mike]

Right checked the wiring alll seems Ok , the only fault I found was within the 3 way valve unit , the earth wire Gr had worked its way lose and was off the contact screw.Retightened and now system runs fine, but I plan to keep an eye on the PCB now its over 5yrs old. So after nearly spending money I was able with this Groups help trace the possible area for attention and resolve without laying out any cash.

My thanks to all that replied , the power of the internet wins yet again.