Yet another boiler question.

[KillerOfThreads]

My boiler is a Main combi 24 HE. The manual says Potterton owned by Baxi.

Over the last 2 weeks the heating pressure gauge was low, so topped it back to 1BAR. Next day down to a half, did the same several times but the same thing kept happening. Bled the rads, some air but not a lot, topped up again but same thing happened so called engineer.

He said i have a leak somewhere on the heating system as that's why the pressure gauge keeps falling. But after a few days watching it i'm not so sure.

The pressure gauge seems to have a life of it's own. One minute on 0, next 1 and anywhere in between no matter if the boilers going or not.Even at zero the boiler is working fine. Yesterday i turned the heating side off and it still read differently every time i looked at it.

Something else i noticed is that when a tap is turned on the gauge shoots up but about a BAR and dropped as soon as it was turned off. I didn't think sealed systems were meant to do that.

The boilers 2 and a half years old and was serviced in October.

I don't want to have to take up laminate floor unless it's realy neccessary.

Any ideas.

Thanks.

[the whistler]

May be due to lack of pressure in the expansion vessel. These do occasionally require topping up with air. As the water in the system heats it expands into the expansion vessel thus maintaining a constant pressure in the system. If the pressure gets too high it opens the pressure relief valve and some water escapes. Then when the water cools down again the pressure drops. You top it up and the cycle is repeated.

I would also consult the experts on DIY - Home Improvement - Do It Yourself

[KillerOfThreads]

Isn't the expansion vessel part of the system i'm refilling to top up the CH pressure?

[the whistler]

The expansion vessel is split into two sections seperated by a rubber membrane with air in one side and water in the other. With the boiler drained of water the air pressure is set at a specific level. When the boiler water heats up it expands and presses against the membrane and compresses the air. This allows water to expand without increasing pressure. As the water cools, it contracts and the air expands to maintain the correct pressure in he system.

If both air and water pressure are set correctly, then a fairly constant pressure should be maintained throughout the heating/cooling cycles.

Occasionally the membrane can be pierced allowing water into the air chamber, which unfortunately means a replacment expansion vessel.

[dazza1011]

Originally Posted by the whistler

Occasionally the membrane can be pierced allowing water into the air chamber, which unfortunately means a replacment expansion vessel.

yes what he said, it shouldnt be too difficult to get repaired.

i had the same trouble and rather than fill up to 1.5 BAR as recommended i had to fill it 2.5 / 3 BAR until it was fixed

[bubbaphatass]

Had the same problem with a Biasi boiler a few years ago, that was the expansion vessel, cost about £80 for a replacement.