combi boiler: plumber mistake?

pardo

After all this, the pressure went down again to 0.5 bar overnight! It seems that changing the PRV and the expansion vessel has not solved the problem. There is no evidence of leaks from any part of the system.

Any advice on what to do now? I guess I cannot keep increasing the pressure back to 1.1 bar every morning.

fezster

What pressure is the EV charged to? (As an aside, was the original checked - it may have just needed pumping up). It should be at around 1.2 bar and the system should be pressurised to around 1 bar. Any expansion of the CH water is then taken up by the EV.
Check the tundish attached to the Pressure Relief Valve - put a tissue there, and see if any water is being discharged.

Dan-Dan

nofoollikeold said:

4. £40 for parts and £140 for 30 minutes labour suggests he / she was charging £280 per hour.  Bit steep even for Central London.  I'd struggle to fit one in 30 minutes, I'd be looking at an hour, more if access difficult.

Alternatively, he charges £140 per hour or part therof

Undervalued

pardo said:

After all this, the pressure went down again to 0.5 bar overnight! It seems that changing the PRV and the expansion vessel has not solved the problem. There is no evidence of leaks from any part of the system.

Any advice on what to do now? I guess I cannot keep increasing the pressure back to 1.1 bar every morning.

The leakage you are looking for can be surprisingly small. When you say "the pressure went down again to 0.5 bar overnight" did you see what the pressure was with the system completely cold at bedtime, or was it still warm / hot? It is far more likely to leak when hot, which is of course when the pressure is higher. 

You can sometime get tiny pinholes which, initially at least, only leak when hot and at higher pressure. The water evaporates off the hot surface so you don't (initially) see any sign of dampness. The pressure drops a bit, but is well above the boiler cut out pressure until it cools down overnight. When stone cold in the morning the boiler then won't fire up. Without wishing to depress you, these can sometimes be a devil to find until they get worse! 

So, your expansion vessel may or may not have been faulty. Did he check the air pressure in it when the boiler was cold? It has a pump up valve, just like a car tyre?

Your PRV may or may not have been faulty however, as others have said, it is often considered good practice to change them along with the expansion vessel or if they have been used manually to let the pressure out of a older / dirty system.

However, unless one of the new items is faulty (can happen) then you must have some other leak that was either the original problem or at least part of it.

Just to add, I am not a gas engineer but I have done a fair bit of plumbing and have chased exactly the problems you have been experiencing on two central heating systems of my own.

Although you are legally required to use a Gas Safe registered person to work on your boiler, any plumber you trust can deal with the radiators and pipework and indeed the expansion vessel now it is external from the boiler!

pardo

You can sometime get tiny pinholes which, initially at least, only leak when hot and at higher pressure. The water evaporates off the hot surface so you don't (initially) see any sign of dampness. The pressure drops a bit, but is well above the boiler cut out pressure until it cools down overnight. When stone cold in the morning the boiler then won't fire up. Without wishing to depress you, these can sometimes be a devil to find until they get worse! 

So, your expansion vessel may or may not have been faulty. Did he check the air pressure in it when the boiler was cold? It has a pump up valve, just like a car tyre?

After reading this I checked the boiler carefully and found a small leak at a compression fitting that connects a copper pipe to a small circular black device with two small electric cables at the back (I guess some sort of temperature sensor?).

Unfortunately access do the nut is restricted and the nut seems to be stuck. So, I have not been able to tighten it - it is actually leaking more now as I disturbed it! 

I suspect this may have been the source of the problem and that replacing PRV and expansion vessel may not have been needed. Anyway, I am going to call a different person to sort this out. Hope I find somebody over the weekend as it is getting cold...

pardo

Just wanted to add, plumber did not check pressure in the internal vessel.

Hasbeen

pardo said:

After reading this I checked the boiler carefully and found a small leak at a compression fitting that connects a copper pipe to a small circular black device with two small electric cables at the back (I guess some sort of temperature sensor?).

Unfortunately access do the nut is restricted and the nut seems to be stuck. So, I have not been able to tighten it - it is actually leaking more now as I disturbed it! 

I suspect this may have been the source of the problem and that replacing PRV and expansion vessel may not have been needed. Anyway, I am going to call a different person to sort this out. Hope I find somebody over the weekend as it is getting cold...

There you go then. Easy cheap quick fix to someone knowledgeable with proper tools.

markin

pardo said:

Just wanted to add, plumber did not check pressure in the internal vessel.

Well then yes you were shafted if thats really true and you never left him alone. But the is always a chance he did it in 2 seconds with his finger and water came out off it and you just didn't see it.