Worcester boiler pump runs for hours

[ShaunCorbs]

Yep I had the same issue which requires a few presses of the resetting etc might be best to wire the boiler into a ups to save having problems

 

[Knappers]

I know it's a bit of a cop-out but what do worcester offer for one off callout.
Do they do no fix no fee or something?
When it comes to just swapping out parts to test, then fixed price repair is definitely the way to go.

 

[ShaunCorbs]

No sorry they get paid for the call out

 

[Don Draper]

Hello, your problem is the module on the side of the motor. I had the opposite problem where my motor would stop intermittently, causing boiler to turn off due to overheat (U1-U9 etc) and motor would not run again until power was cycled. To prove it was the module, I unplugged the purple and black cable plug from module and that gave me your issue, pump runs all the time. I bought a scrap boiler from EBay for £40 for spares and swapped just the module lid, with the PCB in, and hey presto, runs perfect now. Was your replacement pump a new one or refurb? And did it come with a new module on the side? The purple and black cable stops and starts the pump and sets speed for modulation.

 

[Michael H]

The problem with turned out to be a faulty frost stat.
The boiler keeps the pump running when the frost stat activates but will not heat the water until the water temperature drops below 9 degrees.
If you have a frost stat try disconnecting the switch wire in the frost stat to the boiler.

 

[John.g]

Thats the confusion! My gas enginner who serviced it last week put a new PCB on it and was rather lost by the problem. "the pump can only run if the PCB tells it to" was how it was left but the PCB is new. No fault codes or anything. WB are also lost and can only suggest get engineer to phone them when the boiler is opened up to test each component - maybe I will do that next year at its service. It would make sense being frost protection but if it was a sensor or something then I don't get why it only does this if unit is turned on from the mains without a "demand" but if there is a "demand" at time of turning on its all ok and functions normally and its pump turnes off as expected, i would expect the fault all the time. Looks something i will just have to live with, thanks for your help.

The problem with turned out to be a faulty frost stat.
The boiler keeps the pump running when the frost stat activates but will not heat the water until the water temperature drops below 9 degrees.
If you have a frost stat try disconnecting the switch wire in the frost stat to the boiler.

Don't think there's any frost stat as such, when/if the boiler flow temp falls to 8C the pump only runs, if the temp hasn't risen to 9C in 30 minutes then the boiler fires until the
temp reaches 12C and boiler shuts down and the pump switches off.

 

[Vontwinzig]

Update:

I've taken a video:


It shows 24°C in the video before I stepped into the shower earlier. After the shower it was around 55°C, but now 30 minutes later it's only dropped to 53°C, which doesn't seem to be dropping that fast.

I turned the Eco mode off, then back on again, then held the reset button to reset the boiler. It then started to short cycle, and the temperature has now dropped. The boiler is now quiet and remains silent.

What on earth is causing this?

Did you ever resolve this problem? Ours has been doing the same thing, identical to your video.

Thanks

 

[Nick Hawkes]

As I said in my 1st post - the only way I have worked out to stop this is if there is a "demand" any demand, that could be heating, hot water or water heating if eco button is off, as soon as boiler turned on from the mains. So long as the fan & burner run immediatly the boiler is turned on once that initial demand is stopped the pump will stop just as it should after its 3 min overrun period. But without that

I've been having exactly the same problem that you describe. Reading your post about cycling the power with the 'demand' active also worked for me - brilliant!, I hadn't been able to work out why a reset sometimes worked and sometimes didn't. I was on the point of replacing the PCB but from what I read here this would have been a waste of money,

I had some correspondence with Bosch technical support, who were quite helpful. One of their suggestions was that in some installations the presence of small stray voltages on the switched live can cause the pump to run even when there is no demand. At the time I didn't think this explained things because with the switched live disconnected altogether the pump would still run. However in light of your experiences I will experiment with shorting out the switched live input and see if this also stops the continuous pump overrun. I suppose it's still possible that the PCB is sensitive even just to nearby noisy signals.

(The pump seems to be commanded by a PWM signal with a tachometer output back to the controller to regulate the speed. The relevant chip on the PCB has a Bosch logo and from the part number is something originally designed for automotive antilock braking. There is no datasheet that I can find, but the waveforms look 'kinda sensible' to me, so I don't think the pump itself is to blame.)

 

[LongJonSilver]

Hi. I have tried everything you mentioned. No, after about 20seconds from power up it starts its pump (just pump) and runs forever. If CH or HW used during this running that works normally but the pump continues afterwards and continues constantly and doesn't stop after normal overrun period.
As I said in my 1st post - the only way I have worked out to stop this is if there is a "demand" any demand, that could be heating, hot water or water heating if eco button is off, as soon as boiler turned on from the mains. So long as the fan & burner run immediatly the boiler is turned on once that initial demand is stopped the pump will stop just as it should after its 3 min overrun period. But without that instant demant on power up the pump will start after about 30seconds and never ever stop. So unless by chance the room thermostat is turned up & the heating set on on when the power comes off the boiler will do its constant pump running, that means any powercut in summer for sure will send it into its constant pump running.

Hi George4321

This is the only post I have found that describes my exact same problem and thankfully I have used your work around to get the pump to stop. I have a Greenstar 30 CDi System boiler.

Did you ever get to the bottom of this?

 

[John.g]

I remember reading somewhere that some boilers used to keep running with a Y system installation as 70 to 90V is/was remaining on the mid position valve orange wire cured I think my installing a capacitor on the switched live to the boiler or something like that, don't know if this is of any help in the above pump runnin on problem.

"Note: Honeywell and Siemens Y plan valves require a capacitor in the external wiring block or wiring centre to avoid any feedback problems, if there is no other alternative, please contact Worcester Bosch helpline"