Pressure loss on Vokera Excell Combi

[Axel]

G'day, all.

A good friend and client of mine has a Vokera Excell combi. It has been fine until the last few weeks when it has been losing most of the system pressure over a day or 2. She keeps topping up and the engineer her domestic emergency insurance sent was only there for 5 minutes and said there must be a leak in the heating pipework.

This may well be the case. Investigating for such a leak will be a pain in the ass - it's all on the ground floor so no leak will show up downstairs!

I went to have a look and noticed that the expansion vessel had no air charge, so after sorting that it was better but still losing system pressure. The first night it was nearly down to 0 in the morning, the second night it was ok, the third down to 0.5 bar. At no point have I or the client observed any water discharging from the PRV outlet.

It might be a heat sensitive leak in the pipes, but before I lift boards (or mess with the boiler flow / return ball valves which might start to leak), is there any way there could be a leak from the system side of the boiler into the hot water outlet via the secondary heat exchanger? If it was leaking from the cold mains in, then one would expect the pressure to rise, not fall, but if it only leaks as the divertor valve switches over to HW from CH and there is a leak into the HW side then it could theoretically lost the pressure this way.

Am I speculating wildly or is this a known fault?

 

[Tibbot]

Such an internal leak would only lead to pressure rise and discoloured HW. When diverter is closed the path will still be open on the primary return from the plate and still lead to pressure rise. You will have to isolate F/R valves to narrow your search.

 

[Axel]

Good point - the return path...

I will put full bore valves in the F/R pipes just before the boiler and a pressure guage on a 1/2" rad bleed port. That way we can be sure if the CH pipework is leaking or not before shouting at her insurance company.

A lot of boards to take up otherwise...

 

[DP]

I will put full bore valves in the F/R pipes just before the boiler and a pressure guage on a 1/2" rad bleed port

What are you on about. SHows you do not know your boiler or even looked at the boiler manual.

 

[nickso]

has the primary h/e been checked? first port of call on any vokera before any of the above faffing.

 

[Agile]

I will put full bore valves in the F/R pipes just before the boiler and a pressure guage on a 1/2" rad bleed port

What are you on about. SHows you do not know your boiler or even looked at the boiler manual.

has the primary h/e been checked? first port of call on any vokera before any of the above faffing.

Slow down! He said this is a client friend not HIS boiler.

He is not gas registered. But working on the training though.

We know that the likely cause of a slow leak with no evidence of any expernal leak is an HW flange connection within the combustion chamber.

But then we should do as we are registered and often have to go to fix these.

Tony

 

[Axel]

Indeed I am not at all familiar with this particular boiler. That's why I made this post!

I was called upon to find a leak in the CH pipework - that is what the "Heating Engineer" sent by the client's insurance company diagnosed.

I want to be sure that is really what it is before embarking on extensive excavations to find a slow leak that is maybe not there - hence my proposal to isolate the pipework. If the pressure loss is on the boiler side then I will tell the client to call back the other engineer.

This possible leak on the HE flange - is it a leak out of the boiler that should show up as a drip at least, or where would the water be going? As steam out of the flue? Can't remember if it's a steamer or not. I am not proposing to look inside the boiler on this occasion.

 

[nickso]

Slow down! He said this is a client friend not HIS boiler.

doesn't make the advice any less valid.

We know that the likely cause of a slow leak with no evidence of any expernal leak is an HW flange connection within the combustion chamber.

But then we should do as we are registered and often have to go to fix these.

again showing you know nothing. it is far more likely to be the actual h/e that is leaking. there are only two connections in there and none are for "hw".

 

[nickso]

This possible leak on the HE flange - is it a leak out of the boiler that should show up as a drip at least, or where would the water be going? As steam out of the flue? Can't remember if it's a steamer or not. I am not proposing to look inside the boiler on this occasion.

the insulation panels will tell you if you have a leak, one side will be obviously leaked upon.

the two connections may leak if the washers are particularly old but it only takes ten minutes to renew them.

 

[Agile]

Whilst that make does seem to have a prospensity to have leaking HEs I find that the most common cause of leaking is the heating water flange connections. That leaked water is just boiled off whenever the boiler operates so does not show up externally.

Leaking flange joints are particularly likely on a boiler where the system has been depressurised but the pilot light was left on. Or alternatively where the boiler was switched to off so the fan was not running at slow speed.

Usually they can just be tightened up.

Tony

 

[nickso]

i disagree, probably less than 1 in 10 leaks i see in a vokera combustion chamber are the connections.

 

[Axel]

Ok, so (after changing a knacker d boiler isolating valve) I put full bore lever valves on the F / R pipes to the boiler and pressurised whole system it to 1.5 bar cold (the most Thames water would offer at the time.) Then closed the valves and left cold for over 48 hours, and there was no pressure drop on a gauge that I attached to a radiator. Nor was there a pressure drop on the boiler gauge. Boiler gauge might even have risen ever so slightly!

So no leak evident on a cold system.

Not much point in testing hot as the pressure would go down when it cools down (obviously have to open / close the valves to heat it and so lose the isolation of the pipework). So most likely losing pressure in the boiler when hot & evaporating the water?

Any comments?

 

[Axel]

Tony?