In-laws CH and HW does not work

[rallen]

Hello everyone

My in-laws CH/HW system has developed a fault. The boiler starts, stays on for about 30 seconds and then stops. It takes it about 5 mins (roughly) to restart, for another 30 seconds and so on.

They called out the service people who visited and replaced the pump. After that failed to fix the problem they mentioned another possible cause, which however is not covered by the service contract and would cost rather dear to do.

Today I visited to have a look. The boiler is a wall mounted Potterton, quite small. It starts, the flow gets warm (about 40 C) within 30-45 seconds and then it stops. Within 5 more seconds the flow gets cold again, because the pump is working non-stop.

Going upstairs checking the pipes same story: pipes get progressively warm (takes about 30 seconds from the moment the boiler starts), then cold within 10 seconds of the boiler stopping and so on. The 3-way Honeywell valve seems to be working OK, the CH termostat and the HW thermostat are also good.

To verify the pump is working and that we have healthy circulation I did:

(a) it makes the whirling sound (very quiet) and the usual vibration if you touch it
(b) the sound alters as you set it to I/II/III (it is om III),
(c) touching any pipe feels as there is water circulating
(d) progressively closing a gate valve in the HW circuit starts making a hissing sound - of course I did not go all the way to close it completely while the pump was operating
(e) within seconds of the boiler starting there is hot pipes upstairs and they become cold even quicker once it stops

The Potterton boiler has a knob from which to adjust how hot the CH water will get but in any position from 0 to Max it does not do very much (if any) difference.

What would you think the problem is?

 

[REDSAW]

hi welcome.
could be the thermistors gone.

 

[rallen]

thermistor: is that the temperature sensor inside the boiler?

 

[WHPES]

It's not..........by any chance..........one of those evil Potterton Suprima boilers?..........is it?..............

 

[rallen]

One more point about the boiler : we have the manual - it says that to open the front cover you have to remove a screw which however is behind a swinging front panel door - right behind the hinge, so no matter which position the front panel door is at, and without bending the door metal, it is impossible to get a screwdriver to it. What gives?

The boiler is (I just called and asked) Potterton Suprima 100.

 

[WHPES]

Most probably the circuit board will be knackered. Common fault - the quality is awful. Usually manifests by stopping and starting and going to lockout.

Can sometimes be fixed by taking it out and resoldering all the joints on the circuit board (if you are a registered tech). There are companies on the internet doing replacement PCBs at a fraction of the Potterton price.

You need to find one of those worldly wise long established old timer boiler service guys who will have loads of experience.

 

[rallen]

Hi, I have now done a web search and it seems these Potterton Supremas are rubbish. PCBs go every year it seems, symptoms are the same, they fail to heat water adequately even when they work properly, and the replacements are no better.

 

[WHPES]

I think that the independently made PCBs are supposed to be OK.

Potterton used to make good stuff many years ago like a lot of other companies.

Best to buy boilers based on reliability anr reputation rather than price alone - can end up costing far more in the end and a headache for installers.

 

[rallen]

In my in-lasws case they acquired the boiler along with the house when they bought it, not much choice.

I wonder if the service engineer who's visiting tomorrow will actually suggest and TEST the boiler or will he go on a tangent like the previous engineer and suggest "possible sludge in the radiators, not covered in your service contract, 700 pounds please". !!!

 

[WHPES]

If it's going to work out expensive, you could consider putting your money towards updating the boiler to a modern "A" rated one.

 

[rallen]

how much would a new boiler cost? considering that it needs to fit in the same cupboard space as the potterton suprime 100, which is quite small.

 

[Puddle]

The suprima 100 is differant from the smaller models

Still problimatic though

Problem does sound like boiler,as said maybe a thermister

 

[rallen]

Engineer has been, said the hot water cylinder thermostat was loose, put some tape around it and now the system is working properly (apparently). I can not see how the HW affects the CH system, even if the cylinder thermostat has gone nuts, it should be the 3-way valve to deal with this, not stop the boiler completely and prevent the CH working.

He also said the PCB had been replaced in the past (probably by them because my in-laws had no idea).

What gives?