water boiling & spluttering into f/e tank

[progcwj]

Soon after c/h comes on automatically in morning, water circulating from boiler reaches boiling point, creating steam in the airing cupboard, and water in the f/e tank is piping hot.
Shouldn\\\'t the boiler automatically cut out?
If I manually turn down the centrally positioned room thermostat, it clicks and the boiler turns off.
The boiler does not fire up again until I manually turn up the room thermostat.
I have not encountered this particular problem before, the system was installed 20 years ago, new pump & motorised valve fitted about 10 months ago.
C/H system comprises Glow-worm boiler, Horstman Tiara time control, Honeywell programmer & motorised valve & cylinder & room stats.
I suspect the problem is caused by one or both thermostats. Can you help please?
Thanks.

 

[ChrisR]

Sounds like the "boiler stat has gone".
WHich glow worm is it?
What does the thermostat knob look like - blue or white "hat" shaped thing?

Try turning it down.

 

[Whiter]

Is the pump working

 

[progcwj]

To ChrisR:
Boiler is glow worm hideaway 50, stat knob is white hat shape.
Have turned down boiler stat to halfway between max & min.

To Whiter:
Pump is working. For what its worth I have bled pump & all radiators, only one emitted air, all working ok.

Last night I cleaned dust from room stat, replaced. I set time control so that only domestic water in cylinder would be heated in morning, but not the radiators.
In the morning, the domestic water was hotter than usual. I waited an hour or so, then set the timer to turn CH on, after a while (probably less than half hour) there was a rushing noise in the boiler and spluttering into the f/e tank. The tank was hot again and the 15mm cold feed was hot.
I turned the room stat down which switched off the boiler.
I may call out BG to service the boiler - do you think the engineer will be able to solve the problem?

Thanks for your replies

 

[Whiter]

Could be the thermostat on the boiler, does it turn the boiler off when it is getting hot? are the radiators getting hot before it starts spluttering?

 

[progcwj]

To Whiter:
Boiler thermostat does not turn boiler off when it is getting hot.
The radiators are getting hot before it starts spluttering.

If I turn the boiler stat to Min or even to "0" does not turn it off, but turning the room thermostat down until it "clicks" does turn the boiler off.
The fault finding chart in the boiler servicing instructions says "if turning boiler stat to zero does not extinguish main burner, then the gas valve is faulty".

I should probably call out BG engineer to service the boiler, hopefully he will renew the faulty gas valve at no extra charge?
I am still confused as to why the room stat needs to be turned manually to switch the boiler off instead of it happening automatically.

Thanks for your reply.

 

[bathjobby]

I should probably call out BG engineer to service the boiler, hopefully he will renew the faulty gas valve at no extra charge?

If you call them out for a service, you will get a service, not a repair and they won't service a defective appliance. So make it clear what you are calling them out for, suggest repair and service.

The fault finding chart in the boiler servicing instructions says "if turning boiler stat to zero does not extinguish main burner, then the gas valve is faulty".

Probably holds true assuming the stat is working. However, if turning the stat way down low when the burner has been on for some time doesn't cut the boiler out then the stat is likely defective. Gas valve functioning properly is supported by boiler burning on and off under the control of the room stat.

In addition to the boiler fault you appear to have you may want to check the level of the water in the F/E expansion tank when cold. It should be low, just enough to cover the feed pipe running out of the bottom.

 

[ChrisR]

Have found 3 different hideaway 50's, need the GC number to identify it.

 

[progcwj]

To ChrisR:
GC number of Hideaway 50 is 41 313 15.

To bathjobby:
F/e tank is half-full, water level 3 to 4 inches above feed, well below overflow.
I will further test boiler stat later as per fault finding chart which appears to be pretty comprehensive.

Thanks for your reply.

 

[ricarbo]

You could buy a clip on pipe thermosat for about £10 -£15, put it on the flow pipe and see what temperature you've got. If the boiler stat has failed at 20 years it hasn't done badly, really.

 

[progcwj]

I tested voltage between boiler stat & gas valve, after turning stat to "0", and it was still live, which indicates a faulty thermostat.
Maybe room stat was a red herring - time will tell.
Decided on service contract with BG, probably cheaper in the long run.
The boiler was installed Dec 87 when gas eventually arrived here, and had no major problems, so we cant really grumble.
Will post later as to eventual outcome.

Thanks for your replies.

 

[progcwj]

I called British Gas last Wednesday, explained about the problem, i.e. faulty boiler thermostat, and a visit was arranged for the following Monday.
Engineer duly arrived, tested the boiler, said that the stat was indeed faulty, and ordered a replacement, explaining that he could not bring the spare part on the first visit, as policy is for engineer to assess problem on site before ordering.
Engineer then disabled gas to the boiler, labelled it dangerous and informed me that it was illegal to use, quoting gas safety regulations, despite my assurances that I have been turning it off via the time switch for the past week.
The "nanny state" strikes again.

 

[progcwj]

BG engineer replaced boiler stat, c/h system now working fine.