Worcester boiler pump runs for hours

[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"

 

[Art42cdi]

Same problem with a 42cdi caused by a neutral fault on the mains feed (northern power grid). After replacing the pump and fan, this constant pump on problem was present. Turns out to be pcb, the new pcb came with a wiring harness both were replaced and it’s good as new. Hope this helps.

 

[ShaunCorbs]

Same problem with a 42cdi caused by a neutral fault on the mains feed (northern power grid). After replacing the pump and fan, this constant pump on problem was present. Turns out to be pcb, the new pcb came with a wiring harness both were replaced and it’s good as new. Hope this helps.

Yes the new pumps (as Worcester have changed the design) require a new pcb as well deletes the transformer on the back of it etc, the pump should of had a sticker on the box advising this

 

[Kevin McPheat]

Mines the same. I’m no gas engineer but I am an engineer, I supposed I could meter the pump trigger output from the pcb to the pump to see if it’s the pcb causing it. My service guy said it was a known issue between the main pcb and the pump pcb. Anyone found a solution yet?

 

[George4321]

Hi. Thank's for all the suggestions. As it seems quite common there must be a cause & repair known by someone? I am still using my workround of turning on with a demand and then turning off the demand. Did shorting the switched live work for anyone? My boiler does this even if the controller is set for hot water only and heating is off and additionally wether the room thermostat is turned up or down - so if the heating is off on the timer and thermostat is also down I would be suprised to have any stray voltages as that is 2 switches both off on the switched live.

 

[Michael H]

A further update from me, the pump would still run constantly even after the frost stat was disconnected, I have a theory that the boiler was overheating due to the heat exchanger being blocked and that was triggering the pump to constantly run. After several flushing and cleaning of the boiler, removal of the hot water heat exchanger and cleaning with spirits of salts it now seems to be running correctly.

 

[AlunHa]

Worcester Bosch Greenstar 30CDI (2010) - same problem (Pump runs constantly after mains power interruption).

First noticed - approx. 6 years? after installation.
Problem - pump runs continuously after power-cut (no weather compensating controller, no room thermostat).
Issue - if a power cut occurs during period when house is empty, the Pump will run continuously until "workaround" is applied.
Attempted fix(s) - "power off" (of varying length up to 12hrs) or "reset" or adding HW/CH will not solve the problem.

WORKAROUND - Create Boiler demand (Ie HW) during or prior to boiler power up sequence (this is the only thing that works for us).

SOLUTION - Worcester Bosch need to publish better/actionable advice to support this known issue for the installed base.

Thank you to this forum and George4321G for adding a clear workaround.
Concern - I was going to arrange the PCB replacement, but reading that this didn't help in earlier post?

 

[Robert L]

have the same problem. Every time the boiler is turned off at the mains or there is a power cut, after about a min or so, the pump runs, and it runs forever (the burners are not on in this time). During this time if i run a tap or turn on heating it works but afterwards the pump continues to run... forever.
However, I have discovered if a hot tap is running or if the heating is on (and thermostat set to on) before the boiler is turned on at the mains and then turned off a few seconds after the burners start then the pump will stop after its normal over run of a min or so and then stay off. They boiler will then function as normal.
I would still like to find a cause/proper fix to this as I am concerned if we have a power cut when out/away then it will run its pump forever until we return to "reset it".
I have tried resetting the service settings on the PCB to defaults but that makes no difference. I also tried turning off the syphon pre-fill cycle at startup (again in the service settings) that didn't help. I even had our gas engineer change the PCB at it's service and that also didn't make any difference and the engineer had no other ideas as everything else appearked ok at its service.

I have the same problem with my W-B Greenstar 30 cdi. My plumber was mystified by it and phoned up WB to ask their advice, which suggested it was either a faulty pump or PCB, so he has quoted me for replacement of both and labour, but willing to refund cost of one of the parts (pump or PCB) once he has tested the repair and which is the problem part. I am sceptical of this! The problem seemed to sort itself for no apparent reason about 3 months ago after the standard service but then started again after we experienced a power cut about 3 weeks ago. Having just read your thread I tried your remedy above and in fact it seems to work as the pump is now mysteriously working properly again, trning itself off after the usual couple of minutes. Rather than a faulty part I wonder if this is a design fault and WB either dont know about it or are not owning up to it. Thanks for your comment anyway.

 

[Damien]

I have the same problem. Every time the boiler is turned off at the mains or there is a power cut, after about a min or so, the pump runs, and it runs forever (the burners are not on in this time). During this time if i run a tap or turn on heating it works but afterwards the pump continues to run... forever.
However, I have discovered if a hot tap is running or if the heating is on (and thermostat set to on) before the boiler is turned on at the mains and then turned off a few seconds after the burners start then the pump will stop after its normal over run of a min or so and then stay off. They boiler will then function as normal.
I would still like to find a cause/proper fix to this as I am concerned if we have a power cut when out/away then it will run its pump forever until we return to "reset it".
I have tried resetting the service settings on the PCB to defaults but that makes no difference. I also tried turning off the syphon pre-fill cycle at startup (again in the service settings) that didn't help. I even had our gas engineer change the PCB at it's service and that also didn't make any difference and the engineer had no other ideas as everything else appearked ok at its service.
Anyone have any ideas?

George, I have the same problem and your workaround fixes it. Did you ever find out the actual problem. Thanks in advance

 

[George4321]

Very glad the workaround I found by fiddling is so helpful! To answer the question did I ever work out the real cause- no, no idea, had it serviced by two different engineers who (apart from this wierd constant running issue) can see nothing wrong and have no idea of the cause. I am just living with it, and since weston power have replaced some local overhead cables we seem to have stopped getting power cuts. However when we moved in I'm certain the boiler didn't do this. It has never broken down and I can't think of anything that may have occured for this fault to start. As so many people have exactly the same fault I don't understand why there isn't a definate cause & repair identified by WB.
I just can't understand it - I can't see how it's a wiring fault becuase when it is started up using my workaround it is then perfect and stays perfect, if it were wiring wouldn't it recurr every time the affected switch/wiring is live? I guess it has to be to do with something specific that it does during it's startup procedure, some sort of signal/sensor failing to send a signal back to the PCB to tell it to turn the pump off but also something that must work fine the rest of the time as it is completely normal if started in the workaround. Even if turn on without my workaround (so the pump is running constantly) the actual heat output/function for both hot water and heating works fine and turns on & off correctly so it doesn't stop the boiler working.

 

[George4321]

No, never fixed it still living with my workaround that I found by chance fiddling.
2 gas engineers have no clue either, fond nothing wrong generally.
It's not the PCB as had that changed, all that's left to change would be the pump & it's associated control module?
Assume must be some signal that the PCB is expecting during the startup that it doesn't receive - some sensor? But it is odd that the boiler works completely fine if started using the workaround so it can't be something that is completely faulty.
Don't see how it can be wiring as again boiler works perfectly after starting by workaround, if it were wiring it would be faulty every time that circuit is activated.
As it is clearly quite a commmon fault how on earth can WB not know what the cause is?

 

[Philip B]

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.

Has there been any resolution to this please, as my boiler has the same problem.