Worcester boiler shutdown after a few hours

[sambrown1]

I just found this forum and hope someone may be able to help so thanks for any replies

The boiler is a Worcester Senior 6 B/F Combi that has had both a new overheat thermostat and thermocouple fitted recently. After a few hours of running 7 radiators apparently normally it just shuts down and the pilot goes out. It also shuts down after running the hot water and then turning it off - ie when it is switching back to the central heating system. Whilst going through the possible faults before the overheat was changed the engineer linked-out the overheat thermostat and the boiler worked fine and kept going even after running the hot water - hence the replacement. As the problem persisted and the TC was approx. 5 years old the next thought was the voltage from the TC breaking down but as this has now been renewed I am a bit stumped! It is not shutting down due to the overheat kicking out and relights without problem after it has shut down. I suspect a faulty gas valve but would welcome any thoughts. The boiler must be at least 16 years old.

Thanks.

 

[gas4you]

Unfortunately I do not know this specific boiler, but how are you so sure it is still not the overheat?

Especially as it works when linked out?

 

[sambrown1]

Dave

I only say that because the new overheat isn't tripping out either before when the pilot goes out after a few hours of running the rads or after turning off the hot water and it doesn't need to be reset before relighting the pilot - basically it is not reacting as though the boiler is overheating. Are you suggesting that the overheat could be faulty even though it isn't tripping out?

 

[wilder74]

It may well be a build up of carbon in the h/ex.If it was ok when the o/h stat was linked out then it points to when it reaches temp,the boiler cant cope with the excess heat and if theres a blockage it cant push the excess heat around properley,the old 240 were well known for it.Try a chemical clean out

 

[sambrown1]

Hi Wilder74

If what you are suggesting is the case wouldn't the overheat stat be tripping out? If not what else would be causing the pilot to be extinguished which I assume is happening because the gas valve is closing ....

Thanks for your input.

 

[WDIK]

the safety pilot interupter circuit comprises of more than the over heat stat.
but your boiler engineer should know that.

 

[sambrown1]

Hello WDIK

Mmmmm - I would like to think so but due to the age of the boiler there are few heating engineers around that have worked on this model and so there seems to be a shortage of knowledge on what might be the problem .... What else might it be? Oddly, as I have the original manual for it, the wiring diagram shows a number of different therms:, fixed boiler control, control, flow, hot water priority - but the overheat stat doesn't figure anywhere in the circuitry - uuuggghhh??


Thanks

PS Let me assure you that I am NOT messing around with it myself! I don't want to blow myself or anyone else up!

 

[WDIK]

its not out dated and im sure its covered in the basic acs ascessment, so any qualified corgi registered engineer will be able to sort it, if they cant ask to see their corgi card.
sorry but i wont give information on how it works as its part a safety circuit linked to the multifunction gas valve.

 

[sambrown1]

WKID

Your comment about this not being an out dated boiler is the first time anyone has said that - it is the first thing everyone else I have spoken to says first - but I would guess that is because you have been in the buisness long enough to have experience of these older systems. It is your level of expertise that I came here hoping to find and I see from your profile that you are certainly well qualified to comment.

The reason I posted on here was because of just that - talking to a number of heating engineers, their knowledge of how these things work seems pretty minimal. So what I was hoping to get advice on was the logic of why the boiler is doing what it is that might point the engineer to the problem. I can understand your approach on not giving out information for safety reasons and I am very grateful that all of the experts on here are prepared to offer advice for free. However your reticence isn't going to get my boiler fixed which is all I am here for. I repeat I have absolutely no intention of fiddling with this old beast myself!

As I said, it is the logic of the fault finding that I am hoping to understand and at present I am still stumped but about to have the gas valve changed for a not inconsiderable sum. If I can avoid this if it is unnecessary I would be grateful! What I find illogical is why the boiler should shut off after several hours of just running the rads. With the hot water switch over there is at least an event that might be causing the trip but just shutting down after hours of operation seems to me bizarre.

If you don't feel able to point me in the right direction then that is OK and thank you for your input to date but your help would be appreciated.

Thanks.

 

[Agile]

I dont remember ever seeing one of these boilers but I am sure that I could fix it because I do repairs from first principles.

My expectation is that the boiler is overheating and correctly tripping out the pilot light.

A common cause of boilers overheating is as a result of a failure of a pump overheat circuit or thermostat.

Does your boiler manual mention a pump over run stat???

Can you scan and email me with the electrical connection diagram from the manual?

Tony Glazier

 

[sambrown1]

Hello Tony

Thanks for your response.

No, there is no mention of a pump overrun stat - it has a flow stat but i guess that is not the same thing .... ??

Yes, I can send you a scan of the circuitry - what mail address do I use?

Thanks

 

[WDIK]

sorry they bog standard on commercial boilers,

the contacts are supposed to be gold plated to minimise resistance, imit used to be a main manufacturer,
change the leads

an ohm at those voltages is a hell of a lot.

 

[sambrown1]

Hello WDIK

I think your last was destined for another thread .....

Regards

 

[WDIK]

why?

 

[sambrown1]

WDIK

Now I AM confused! Was your comment about something being bog standard on commercial boilers and gold plated contacts really in response to my thread about an over-heating Worcester combi that you contributed to yesterday - if so I am way out of my depth ....