Boiler overheating

[teecee90]

Can anyone please help. I have a glow worm 18sxi boiler that is 7 years old and has been nothing but trouble. Latest problem has been an overheating issue that has been going on for over 3 weeks and had so far cost almost £800 in repair bills and is still not fixed. First visit diagnosed a faulty pump. Pump replaced at a cost of £385 but fault returned after a few days. Next the thermistors and overheat stat were replaced but that seemed to cause another fault to the PCB which was later replaced at a cost of another £387. Fault returned again so a second thermistor has been replaced but the fault returned again today.

I have noticed that the overheat fault seems to occur when the timer switches the boiler off. The pump seems torun on okay but the water doesn't seem to be able to flow. Any ideas please? I'm getting to the end of my tether!

 

[Chalked]

Has the system got a by-pass fitted?

 

[hammers4spanner]

£800 in repair bills are you mental!!!

 

[teecee90]

The pump was £195 + VAT
PCB was £215 + VAT
Thermistors and overheat stat were about £60 + VAT

The rest was labour and initial call out charge.

The boiler instructions do show a bypass valve on the parts list.

 

[teecee90]

Has the system got a by-pass fitted?

There is a bypass valve shown on the parts list in the boiler instructions if that's what you mean?

 

[teecee90]

£800 in repair bills are you mental!!!

Possibly! having used the same company to service and repair the boiler over the last 7 years you sort of assume that they know what they are doing and wont rip you off.... They are a well known and long established local company.

If I had known it was going to cost this much I might have been better off just getting a new boiler fitted. Its only 7 years old but has been problematic since day 1.

 

[jtsplumbing]

If it been a problem since 1st fitted then could be a install fault ! you should have got a price for doing the repair first , if that had been one of my customers I would have advised getting Glow-worm out on a fixed price repair (About £250) think I would be asking why the repairs cost so much, looks like they are just throwing parts in it when not needed.

 

[teecee90]

If it been a problem since 1st fitted then could be a install fault ! you should have got a price for doing the repair first , if that had been one of my customers I would have advised getting Glow-worm out on a fixed price repair (About £250) think I would be asking why the repairs cost so much, looks like they are just throwing parts in it when not needed.

Its a different problem each time. Since installation it has had a new PCB, new pressure release valve, new expansion tank, new flue collector assembly and now another PCB, pump, thermistors and overheat stat.

I've been speaking to another local plumber today. He mentioned the Glow-worm fixed price repair (wish I'd known about that before!) but thinks it is not a boiler problem anyway! Having talked me through several checks he thinks it is most probably a problem with the 2-way motorised CH valve. Grrrrr meaning that £800 was a complete waste of money. He suspects that the PCB may have been damaged by water leaking onto the PCB when the previous cowboys changed the pump unnecessarily.

 

[jtsplumbing]

Its a different problem each time. Since installation it has had a new PCB, new pressure release valve, new expansion tank, new flue collector assembly and now another PCB, pump, thermistors and overheat stat.

I've been speaking to another local plumber today. He mentioned the Glow-worm fixed price repair (wish I'd known about that before!) but thinks it is not a boiler problem anyway! Having talked me through several checks he thinks it is most probably a problem with the 2-way motorised CH valve. Grrrrr meaning that £800 was a complete waste of money. He suspects that the PCB may have been damaged by water leaking onto the PCB when the previous cowboys changed the pump unnecessarily.

Mate you have been stitched up big time, and would be asking some questions of people who have been messing with your system

 

[teecee90]

Im waiting for a firm solution to the problem and will then be going after the cowboys that have stitched me up.

Im starting to narrow the problem down now. The overheat only happens when the room thermostat detects that the house is up to temperature. It seems that the room stat sends a signal to close the motorised CH valve but the boiler keeps running for some reason. The water obviously cant circulate so the boiler overheats and trips off. Although Im still not sure where the fault is. Would it be a faulty motorised valve or faulty room thermostat or something else? If anyone can point me in the right direction I would be really grateful.

 

[MC_Bob]

As a company if we misdiagnose a repair we don't charge for it..

 

[teecee90]

As a company if we misdiagnose a repair we don't charge for it..

Laudable. But when was the last time you were challenged on your diganosis, admitted to an error and issued a refund?

In my experience it is very rare for any tradesman (plumber, electrician, mechanic etc) to admit to any sort of error, even when it is staring them in the face. I have challenged the company but they maintain that all the parts they have fitted were absolutely necessary and even if the 2-way valve is faulty it is just one of multiple genuine faults.....

 

[dancinplumba]

Im waiting for a firm solution to the problem and will then be going after the cowboys that have stitched me up.

Im starting to narrow the problem down now. The overheat only happens when the room thermostat detects that the house is up to temperature. It seems that the room stat sends a signal to close the motorised CH valve but the boiler keeps running for some reason. The water obviously cant circulate so the boiler overheats and trips off. Although Im still not sure where the fault is. Would it be a faulty motorised valve or faulty room thermostat or something else? If anyone can point me in the right direction I would be really grateful.

As Chalked has said, have you an external by pass ?

 

[teecee90]

As Chalked has said, have you an external by pass ?

I've asked plumber number 2 and apparently not. Its been that way since we have lived here (about 8 years) and the house is about 15 years old so presumably it has never had one and not caused any problems before.

Is the lack of a by-pass likely to be the cause rather than a faulty CH valve then?

 

[jtsplumbing]

This boiler has a built in by-pass, its possible that the by-pass tube is blocked remove tube and see if its clear and that by-pass valve is ok,

 

[Pongo]

What is the service history of the boiler and has the system had a powerflush in the 7 years its been installed? Mucky systems can play havoc with boiler internals.

 

[Bolty123]

I don't think the hxi has a built in bypass it's heat only. Think your valve end switch sticking
your original plumber is a joke.

 

[Bolty123]

Sxi not hxi sorry listen to jts reply. I'm talking rubbish again.

 

[jtsplumbing]

I don't think the hxi has a built in bypass it's heat only. Think your valve end switch sticking
your original plumber is a joke.

OP says it's S-xi (System) not H-xi

 

[teecee90]

It does have an internal by-pass but everything is totally clear. The system has a magnaclean fitted and when the pump was replaced the engineer said it was completely clean.

As I said previously, it only overheats when the room thermostat tries to shut the system off. When the timer shuts it on and off everything works okay.

The way it was explained by plumber 2 is that when the room thermostat gets up to temperature it sends a signal to the 2-way motorised valve which closes the valve. The valve also has a microswitch which then shuts the boiler down. If the valve /microswitch is faulty it is possible that the valve is closing but the boiler continues to run causing a lack of circulation and overheat of the boiler. I assume that the bypass in the boiler itself wont stop this from happening if the burner is still running at full wack? Any views on this? Is it plausible?

He checked the 2-way CH valve and tried to open it manually with the lever on the side - but it wouldnt move....although it does seem to move okay when it gets a signal from the thermostat. The HW valve moves much more freely and could be opened manually with no problem.

 

[teecee90]

Forgot to mention that when the room thermostat gets up to temperature and clicks off, the boiler starts to get noisy and clancks and bangs before overheating and tripping out to F5 error.

 

[Chalked]

It's an easy check, but must be carried out by a gsr engineer if checking at the boiler or an Electritian with heating experience.
to prove your theory ( likely to be correct) it's a matter of checking if the boiler is receiving a switched live after everything is turned off.
your plumber should have checked for this.

 

[plumbdoctor]

Pump overrun not working correctly ?

 

[snowhead]

Pump overrun not working correctly ?

It seems like it's been wired so the stat kills the power to the pump and it never gets pump overrun.

 

[teecee90]

Update

Well....its taken about 6 weeks but the problem is finally fixed (fingers crossed). After getting a second opinion the first plumber confirmed a faulty 2-way CH valve and has today replaced it free of charge. They still claim that the replacement Pump and PCB was necessary but have given me a £100 refund as a goodwill gesture. Everything seems to be working well now.

Replacing the CH valve was quite a big job though as the valves are tucked behind the HW cylinder meaning the cylinder had to be disconnected and moved out of the way to get access to replace the valves. Apparently a really bad design when the house was built.

I had the HW vale replaced at the same time as a precaution. The new valves are apparently serviceable without having to be removed so if they develop another fault later they can be repaired without having to remove the HW cylinder.

Thanks to everyone that contributed to the thread.