Boiler problem not repaired by plumber - advice sought

[Martin J. Evans]

Hi,

I realise we are talking boilers here and I'm not after any advice on DIY boiler repairs as I'm not qualified. However, we had a boiler problem and paid a gas safe engineer to fix it but it is not fixed and so I'd appreciate any comments on the possible problem.

This is a Worcester Bosch green star highflow 440. The symptoms were that the pressure is usually at around 1.5 bar (recorded with the red pointer on the meter). When the boiler was serviced the engineer noticed the pressure was way down and topped it back up via the filling loop. When the boiler was turned on, the pressure increased as the water temperature increased until it reached around 3 bar and then water was expelled outside.

He said the integral expansion vessel was broken. He explained as the water heated up it expands and the expansion vessel is supposed to take up that increase. As the pressure got to 3 bar he said our expansion vessel was obviously broken and offered to repair it for £110 + vat (parts) and 1 hours labour (it didn't take anything like 1 hour by the way). He arrived yesterday to fit it and I was not in so I could not see what was done and my wife didn't pay any attention.

This morning I notice the pressure is right down again. Water is being expelled outside just as before.

Any comments?

Martin

[charles]

He probably included travelling time. It doesn't come free.

It sounds as though it's overheating.

[Martin J. Evans]

That is fair enough - I wasn't really complaining about the cost. What he actually said is the charge is per hour or part of.

What is over heating?

Is there anything which indicates this? I notice the water temp for the heating got to 70C but I think that is usual as the setting for the heating temp has not been changed and the position of the dial is below the E mark which is documented in the owners manual as 75C.

The pressure reaches 3.2 bar before water is expelled.

Thanks for the comments Charles.

Martin

[charles]

'Overheating' meant the boiler is getting hotter than it's supposed to. According to one of the laws of physics (Boyle's?) (A-level was 53 years ago), with a fixed volume pressure will increase with temperature. If you pressure is rising unusually, then it would seem logical that the temperature is also rising.

This seems to imply the temperature is normal, so it must be something else. Perhaps somthing is preventing the water circulating properly

[Andrew Gabriel]

Given the reported symptoms, his diagnosis sounds correct.

Expansion vessels fail in two ways: The internal diaphram punctures so it can no longer retain the air cushion. The air leaks out of the air cushion through the tyre valve on the pressure vessel.

In the first case, the vessel needs replacing. In the second case, the vessel needs pumping up again with a bicycle pump.

It may be that he did one or other of these - ask him. If the pressure vessel is inside the boiler, it's often easier to just ignore it when it fails, and fit a second one outside the boiler.

Assuming he did fix that, the options I can think of are: The new vessel isn't working - I wonder if it was pumped up (although the only one I've ever bought came pumped up, but I suppose it could have gone flat in the warehouse).

Some debris has got onto the seat of the pressure relief valve, and is stopping it fully closing. This can happen if it lets any water out. You could try filling the system up to its normal pressure and see if it is still expelling any water, when it shouldn't be. If it is, try momentarily opening it to see if that will shift any debris stuck on the valve seat.

[Ghostrecon]

its the pressure law - P and T

Boyles - P and V

Charles - V and T

[geoff]

In message , Andrew Gabriel writes

Andrew's reply is almost exactly what I would have said

Ignore the other replies, they are not relevant

[Roger Mills]

How much did he actually charge you? How long was he there? Can you see any evidence that he actually fitted a new vessel?

My guess is that he simply pumped up the old one in the hope that the air simply needed re-charging. In the event, the diaphragm was shot - so re-charging didn't fix the problem.

If he claims to have fitted a new one, ask to see the old one!

Oh, another thought. Maybe he *did* change the vessel but maybe there was nothing wrong with the old one - but simply a blockage in the connection pipe.

Can you identify and access the pressure vessel? If so, use a car pressure gauge to check its charge pressure with the water system de-pressurised. If all is well, I would expect to see about 10psi. If water comes out of the valve, you've definitely got a problem!

Then re-pressurise the water system with the filling loop. It should take several litres of water to bring the pressure from zero to 1.5bar. If the pressure rises very fast when you admit water, it indicates a lack of expansion capacity - usually a shot vessel, but could be a blocked pipe.

[GB]

When you get it sorted, get the inhibitor level checked as well.

[Frank Erskine]

A plumber's hardly the person to be diagnosing faults in a boiler. No disrespect to plumbers, who are the people who fit/mend the pipes to distribute (normally) water (and who usually make a very good job of it!).

[Brian Gaff]

Either that or the pressure detection is not working correctly. Brian

[ARWadsworth]

Odd that he got someone in to service the boiler and not repair the boiler!

[Martin J. Evans]

He never told me that - he just said it was broken and needed replacing. He said it was punctured and I didn't see him try pumping it up again. I also asked for any replaced parts to be left behind but he did not do that. The bill says the vessel was replaced - cost £110 + vat for part.

it is. It is a rectangular metal box about 16" * 12" and around 2 - 3" thick on a hinge that allows it to swing out. It has a metal hose in the top and what looks like it could be a small valve - difficult to see without swinging it out and I've not done that.

I see mention of that in the manual - under fitting a second pressure vessel. There is not really room for that.

Interesting - I don't know.

No water is expelled when the system is pressurized to 1.5 bar. As the heating comes on the water heats up and the pressure starts rising. At around 70c the pressure is 3.2 bar and water is expelled (a lot of water). When the heating is off and no water is being expelled there is a small round pressure release valve and when that is turned water is expelled - it springs back to closed when you release it.

What I don't understand is that water was being expelled when I got home and that was only 1 hour after he left. It is almost as if he did not actually test it. I will have to get him back.

Thanks for you input.

Martin

[Martin J. Evans]

I did not know it was broken. It was a yearly service and the person servicing it said it was broken and offered to repair it. That was not clear in my original post.

Martin

[Martin J. Evans]

£110 + vat for new pressure vessel. 1 hour labour. He was here around 30 minutes.

Evidence of new vessel - not really. I could not say for definite it is a new one - the old one looked perfect to me - no scratches or even dirt on it. It is the first thing you see when you remove the cover. I meant to put a scratch in it but forgot. I asked him to leave all replaced parts but he didn't.

I cannot even see evidence of spanner scratches on the nut that secures the metal pipe into the top of it. Undoubtedly, the valve cover on the top has not been removed as it has been painted after fitment.

There is a metal pipe going in to the top and then a small valve with a screw on cover. The valve cover is painted and does not look like it has even been unscrewed.

Yes

To do that I'd have to unscrew a cover over the valve. Am I violating any law doing this. Looking at the valve screw on cover it looks as though it has been sprayed with paint after being screwed on - as if it was all assembled except the pipe fitted then sprayed in the factory.

I've not yet tested the pressure in the vessel as to do that I'd have to unscrew the valve cover and as I said above it looks like it has been spray painted after being screwed on.

It does take a lot of water to re-pressurize the system and the pressure rises quickly but no quicker than I remember from in the past when I've topped it up after a radiator replacement.

Thanks

Martin

[ARWadsworth]

Did the boiler work before he arrived first time and topped the pressure up?

[Martin J. Evans]

I'm not sure if you are referring to the people in this thread or the person who came to service my boiler. I called the person who serviced our boiler and diagnosed the fault a plumber - perhaps I should have used some other job title. I've no idea who the people in this thread are (although I am grateful for the comments) but the company who sent the person to service our boiler is gas safe registered and I checked the gas safe web site, I can see the picture of the person who they sent and he is qualified according to gas safe (can't remember all the qualifications he had but there were around 10 or so including commercial and domestic. I chose the company because of the above and they are local(ish) and their web site says they are registered Worcester Bosch installers.

Martin

[Martin J. Evans]

Yes it was working in that our radiators were hot and we got hot water. The boiler is in a cupboard and you cannot see the pressure gauge without removing the cover so it is not something I keep doing. It is possible it was under pressure for some time. I'd not noticed water being expelled but the pipe on the outside is at the side of the house and not something I pass regularly.

The heating works now - in that the radiators get hot. On arriving home after the vessel replacement I checked the pressure and it was around

1/2 of the 1.5 bar the pointer is set at. When I went outside it was obvious water had been expelled. On topping it up again and switching the heating on a lot of water was expelled again and now the pressure is back down at 0. This does not seem to stop the heating coming on or the radiators getting hot. There are no error conditions shown on the display.

Martin

[ARWadsworth]

A faulty pressure gauge would be a good bet.

[Andrew Gabriel]

That gives me another thought - he might have fitted one which is smaller than the original, and isn't big enough for the system.

I would expect it to have the size (normally capacity in litres) written on it, and you could cross-check with the boiler spec for what the original size was. I would also check the manufacturing date if it says, just to see if if was changed at all.

I fill my system to 1 bar when the water is at 20C. 1 bar is enough to fill a system to 30 feet above the height of the guage (33' in theory, but you need some excess to allow bleeding highest radiators). What is the height difference between the pressure guage, and the highest part of your heating system? Unless the guage is on the bottom floor of a 3-storey house,

1.5 bar cold pressure sounds unnecessarily high.

When the system has cooled back to ~20C, what does the pressure drop to if you don't refill it?