Boiler losing pressure

kevinheb

We have an Alpha CB28 combi boiler installed. Since we moved in last year, it has slowly lost pressure over time, and we've had to either top up the system using the filling loop or add more air to the expansion vessel.

I had thought that the problem was a leaky expansion vessel, but a few weeks ago I was unable to pump up the expansion vessel anymore, despite trying several pumps. When I say unable, when pumping air into the expansion vessel there was already some pressure in there, and when I pushed the valve in air hissed out, but I couldn't seem to add any additional air - it felt that either the valve was blocked or that it was already at high pressure. I was back to using the filling loop, which I'm aware is less than ideal as introducing fresh water to the system will encourage corrosion.

I turned the system off a couple of weeks ago, added water through the filling loop to 1.5 bar and left it. Over the past 2 weeks, the pressure has slowly decreased, and it is currently at 1 bar. Does this indicate that there is a leak somewhere within the boiler. Or would it indicate that there is a problem with the expansion vessel, or something else?!? Any advice would be much appreciated.

macman

A leak on the boiler should be visible. But there could equally be a leak anywhere on the CH circuit.
Have you checked the PVR overflow to see if it is escaping there?

gas4you

Could be a faulty valve on the expansion vessel.

You need to check out macmans post first as well.

Tape a plastic bag over the prv outlet and check a few days later for any water in it.

It could also not be the expansion vessel, but the pipe connecting it in the boiler that has become blocked, so the symptoms will be the same as a knackered EV

Mr_Ted

No one has yet asked the question, how did you attempt to repressurise the expansion vessel?

Did you drain the boiler to repressurise the Expansion vessel?
What pressure did you inflate the expansion vessel to?

If you didnt and the expansion vessel still has pressure in it then you may be overpressurising it, which will mean as the system water heats and expands the safety valve will blow as the expansion vessel cannot take any pressure above what is already in it?
Or if you are trying to pressurise the expansion vessel against the system pressure(boiler not drained) you will not be inflating it to the correct pressure?

kevinheb

Many thanks for your help, I'm working down the posts in order. I'm having difficulty locating where the prv overflow pipe; a pipe runs down from the prv outlet on the boiler and goes through the floorboards, there is a thin plastic pipe that comes out below the bathroom window (below where the boiler is situated in the loft) and that is the only pipe that I can see that is not connected to anything.

I tried closing the prv pipe by turning the valve off with a screwdriver but the valve would only turn about a 1/4 of the way round (bear in mind the boiler is currently off - I'm aware of the implications of turning it off while the boiler is operating), as I was hoping that might isolate a fault with the prv

gas4you

kevinheb wrote: »

I tried closing the prv pipe by turning the valve off with a screwdriver but the valve would only turn about a 1/4 of the way round (bear in mind the boiler is currently off - I'm aware of the implications of turning it off while the boiler is operating), as I was hoping that might isolate a fault with the prv

I hope you have got the wrong pipe :eek:

The prv should have nothing fitted to it, especially a valve that can be shut.

If it is indeed correct what you have said, then your boiler is extremely dangerous.

kevinheb

Sorry, yes I did have the wrong pipe, it comes out at the back of the house at the bottom of the roof. Is there an easy way to monitor it because the pipe is about 20 feet up?

mattmk6

Im interested in why you are adding air to the expansion vessel to re-pressurise the system and how you are doing it?

A common problem to check for is to take the plastic caps off the radiator valves and check for water. These can hide the water very well as the odd drip every few hours will run straight down the pipe and under the floor.

Is it a replacement combi or did you have a header tank in the loft previously? Somethings when converting to a sealed system can cause leaks due to the extra pressure within the system

kevinheb

hi mattmk6, I'm adding air to the expansion vessel with a foot pump, as it has a schrader valve, I thought that air was escaping through the valve, causing the system pressure to reduce, so I was pumping air into it, which causing the system pressure to increase.

southcoastrgi

kevinheb wrote: »

hi mattmk6, I'm adding air to the expansion vessel with a foot pump, as it has a schrader valve, I thought that air was escaping through the valve, causing the system pressure to reduce, so I was pumping air into it, which causing the system pressure to increase.

have you released the pressure within the boiler ie draining it before you pump up the expansion vessel ?

kevinheb

No I haven't Keith, many thanks for the suggestion, i'll give it a try at the weekend