Hot Water Problems

[Dugarry]

Hi all,

Looking for some advice.

Problem is the DHW from my combi boiler (Potterton Performa 24) keeps fluctuating between hot and cold.

Symptoms are that the water runs warm, hot, very hot and then the boiler shuts down. The cycle starts again after a period as the boiler realises there is still demand for hot water.

There doesn't seem to be any pattern to when it does this. By this I mean it's the same whether central heating is running or not. How bad it happens does vary though, somes days it won't happen, others it will run cold (boiler shutdown) every couple of minutes.

I'm at a bit of a dead end. After reading lots of useful posts, having an independent engineer out to have a look as well as four visits from Bristish Gas, I've been left with the boiler still playing up and no consistant idea of what the problem is.

I have replaced the secondary heat exchange + cleaned and flushed the system. Slight improvement resulted but not fixed and it's getting worse again.

I'd appreciate any help or hints.

Could it be a temperature sensor? Or faulty PCB? The hot water temperature doesn't seem to vary when I turn down the hot water thermostat...

Thanks for taking the time to read, you'll be helping a frustrated household!

 

[gavinda]

if you're on contract with bg then just get them back again. what did they say the issue may be?

 

[bengasman]

how did you flush the system?

 

[cider]

thermister problem?

 

[Agile]

Having an independent engineer "out to look" is intreaguing!

Did he charge for his visit on which he was unable to diagnose the fault?

Three BG visits! Not the competence their ads lead you to believe they can provide! After the second they should have called a more senior engineer! Or was he unable to solve the problem either?

Boiler repairs require a logical approach which involves making many measurements on the boiler to identify where the problem lies.

A proper thermal survey will usually easily identify problems like that. Did any of the BG guys even measure ANY temperatures? If not then what did they do?

I dont know whats wrong with your boiler but I am sure that I could find the fault within 35 minutes on site!

Tony

 

[gavinda]

Three BG visits! Not the competence their ads lead you to believe they can provide! After the second they should have called a more senior engineer! Or was he unable to solve the problem either?



Tony

i agree agile. but i cant see why we didnt sort it. usually when we start a repair job we finish it. ive only ever called it quites when the boiler is fubar or an ariston . every other time ive succeeded. not allways 1st time, but eventually

 

[Dugarry]

Thanks all for the replys...

I used a fernox cleaner and then mains water flush + retopped with fernox inhibitor.

3 separate enginners visited from bristish gas, 1st said it could be the heat exchangers.... hence changing the secondary (I know there is a primary one also, that hasn't been changed due to cost compared to boiler!)

2nd visit along the same lines as the first visit however was stumped when I said the heat ex had been replaced, after saying it was down to scale in the system, so I should replace the in line lime scale remover.

3rd visit said it was due to water flow not being at the "ideal" 9.8l/m as stated in the manual... after a bit of digging on here I found the minimum flow which the boiler requires.. something like 2.8l/m, so another false lead. He even said to get hold of the water board and see if they can increase supply to the house.. erm yeah right! This visit was just before Christmas so I'll let him off.

I understand BG's policy around the heat ex's, they won't cover these parts unless they are new / been replaced by them, however, with the cost quoted to supply and fit the seconadry (£200) I dare not go down this route!

Boiler is about 6 years old, from what I gather having moved into the house a couple of years ago. Problem wasn't evident back then.

No temperature check have been run on the boiler.

Any contacts someone can provide me with as an independent 'competent' engineer who will come and have a look?

Yes - independent engineer I was recommended did charge £60 cash, first time was for a service, second time just to look, take out the old secondary heat ex and bang it around a bit.

 

[gavinda]

was ther any improvement when the heatr exchanger was 1st replaced and how long till it gotworse again. ive had quite a few jobs where the system wasnt flushed and the new heat ex was blocked within a month.

 

[Dugarry]

So... it appears fixed.

Just to update the post incase someone is reading with a similar problem and looking for answers...

Apparently the gas being supplied to the system was too high / too much.

Credit to the British Gas engineer who stuck with it this time and has managed to fix the problem. The hot was not stays at a constant and the boiler is not switching off.