Ever Increasing Combi Boiler Pressure

[cwcw]

Hello.. my boiler (a "favourite" of this forum - Heatline Vizo combi boiler) seems to have a problem with the pressure. It is gradually increasing over time. The boiler is about 18 months old. At first it wasn't noticeable, but over time it has become worse, to the point now that it has increased from 1.3 bar last weekend (when I drained the radiators down from 3 bar) back up to 2.5 bar, within the space of a week!

I have been advised in the past to leave the filling loop disconnected. The problem with this is that the filling loop when disconnected from the tap permanently drips, apparently out of the boiler as the pressure drops very slowly. Last winter I left it dripping over night and by morning the pressure was about 0.5 and the heating wouldn't come on! I Had to reconnect and refill. Therefore I leave the filling loop connected, since it can only leak as far as the refill tap, which plugs it. Could this be related?

It might also be worth mentioning that when we first moved in and no-one knew how combis worked, a well meaning relative turned the filling tap on and left it on, thinking that was how it worked. This found a weakpoint in the pipework and leaked massively from the pipes because the pressure got so high. It was on fill for probably about 5 mins before the leak was noticed. Could this have damaged something? This was about 16 months ago.

Other than the pressure problem, the boiler performs quite well - water is hot almost instantly, the shower has a good heat and pressure, and the radiators all get hot within minutes. It was professionally installed before we moved in. We have the Corgi cert for the boiler and plumbing installation. Think that covers everything!

Thanks

 

[AMEdinburgh]

From a DIYer not a plumber.

For the pressure to go up there has to be a source of new water entering the combi / rad system and the only source, I would have thought, is the filling loop unless there is something really odd going on. Even if the filling loop is dripping slowly, that means quite a volume over time and it will force it's way under mains pressure into your heating circuit.

I would be suspicious that your filling loop is not completely switched off or the valve is leaking. The seal from the boiler might be leaking also but that would decrease the pressure if allowed to drain and is probably not significant in your difficulty but could do with being fixed.

Prob best to wait for the experts but hopefully food for thought.

 

[cwcw]

Thanks. Any advances on that anyone? Or is this a really rare and expensive problem?!


Cheers

Cathy.

 

[muggles]

Ever increasing pressure is normally caused by one of two things:

1) Leaking filling loop. This seems to be the case with you, and having your plumber replace the faulty valve (you're not allowed to do it yourself if it's part of the boiler) would be a great start. If you can put up with it for a bit longer, and the annual service isn't too far away, make him aware of the problem and he can replace the valve when he services your boiler. EDIT: Sorry, just re-read and see that your boiler is 18 months old, so presumably you're between services at the moment. Probably best to get it sorted now if you've got that long to wait.

2) Internal crack in heat exchanger, which is the bit that transfers heat between your heating and hot water systems within the boiler. If this is split, the waters can mix, and usually this means that the hot water will leech into the heating system, thereby increasing the pressure. Try fixing the other problem first, if that doesn't solve it then you'll need a new heat exchanger.

 

[Agile]

Because the Vizo is the cheapest boiler on the market, they are usually installed badly! We charge over TWICE the cost of a Vizo to install one! But then we do it properly and they would never give any problem.

I would guess that the filling loop and its valves were not replaced with the boiler as woud be the normal good practice.

If this is the case I suggest that you get the installer to replace the filling loop ( free! ).

If that does not solve the problem then it is probably the plate heat exchanger leaking. This would be a manufacturer's fault and therefore covered by the warranty. I hope the installation was registered with the manufacturer or if not that you have the original purchase receipt for the boiler.

Tony Glazier

 

[cwcw]

Unfortunately the boiler was installed before we moved in, and the warranty for it was only 12 months anyway.

 

[WDIK]

dis the fill loop its against water regs for it to be connected anyway.

then see if it rises

 

[cwcw]

dis the fill loop its against water regs for it to be connected anyway.

then see if it rises

I have been advised in the past to leave the filling loop disconnected. The problem with this is that the filling loop when disconnected from the tap permanently drips, apparently out of the boiler as the pressure drops very slowly. Last winter I left it dripping over night and by morning the pressure was about 0.5 and the heating wouldn't come on! I Had to reconnect and refill. Therefore I leave the filling loop connected, since it can only leak as far as the refill tap, which plugs it.

 

[cwcw]

Just to add to the above, a deep hot bath has just added 0.1 to the pressure. The heating has not been on at all. I think this means it's the heat exchanger then? Anyone any ideas how much this would be (+labour) for the Vizo?

I think the leak from the boiler out of the filling loop is a separate problem which will need a new valve (this leak is definitely water from the heating system itself and lowers the pressure, i.e. not a leak the other way round from the mains supply).

 

[Agile]

Its normal for the pressure to increase by expansion when the boiler is heated up.

Do as we tell you to replace the filling loop as its clearly faulty anyway.

I expect that you will then find that the pressure increase has been miraculously cured!

Tony