Low water pressure in combi boilers

Could it be to do with the pressure of your water supply rather than a problem with the boiler itself?

We have a combi boiler too but had ot replaced a couple of years ago. The old one used to lose pressure a lot. The current one doesn't.

So, in short, ?‍♀️

I find that my boiler can go off in summer so it is definitely something to do with the pressure being up when the boiler is running. I know the water level drops more and more when the boiler isn't on.
Not much help but seems to happen to combi boilers as all my neighbours have the same issue.

When I had my boiler replaced I would have liked a combi boiler for reasons of space, freeing up a large are of kitchen however my CH pipes were in the concrete floors so was told the increased water pressure would be too much for them.
I have lived to be grateful for that as two of my friends seem constantly to have the problem with the pressure dropping and frequently have a plumber visit as either can do it themselves.
I cannot answer your question, sorry , but just to say it seems a common problem.

I wouldn’t know where to start. I have a combi boiler, but how do you “add” water ? Where?

crazyH, there is a tap on the actual boiler, or possibly two taps, which you just turn to add water. They are somewhere on the incoming water pipes. If you have a display on your boiler, it will show you the water pressure gauge.

Have a look at the operating manual as there should be a labelled diagram of all the icons on the display and also where the taps are.

It’s worth knowing as it is an easy fix, but very annoying first thing in the morning!

I do have low water pressure, the plumber mentioned it when he installed the boiler, but not too low as he still recommended the boiler and it’s been serviced every year.

I’ll have a think about the water pressure and discuss it when next serviced.

Thankyou Teachername x

We had our pressure valve replaced on ours a few weeks ago, similar problem.

Teacheranne I have the same problem but my boiler is in the loft - every few months I have to pull down the rickety ladder and struggle up there! I just turn the water valve on until the pressure is right and then turn it off.

I have asked the heating engineer what can be done as I’m not getting any younger to climb up there. Apparently it could be a slight leak in the system somewhere. We have checked all the radiators but no leaks. Suggest you do the same as it might solve the problem for you. It’s no joke when there’s no heating or hot water.

The expansion tank in a combo boiler is quite small yet to how it heats small amounts at a time that then feed to your heating system or to your hot water supply. Inside the tank is a diaphragm that when the heat in this small tank builds up will vent to an external point Sometimes the diaphragm will move too much to fully return to normal and so it will continue to vent at lower pressures. When the system cools down overnight the internal pressure naturally drops leaving less water in the tank than before any venting.

‘That is how’ not ‘yet to how ‘ grrr

It does seem to happen a lot....to some boilers more than others, ours is an Ideal ( won’t have another one!)
There’s an internal cylinder which combines air and water, and sometimes the air pushes the water out.This then needs an engineer to clear the system out and rebalance it.
There could be a leak ( the other explanation) so check all the radiators.
DD has a combi boiler which she inherited with the house and is about 12 years old, no probs whatsoever.Ours is only 7 years old and we have this prob frequently.

We have this problem sometimes and had to go into the loft to turn on the little taps that raise the pressure. Recently we paid a plumber to bring this feature downstairs into the airing cupboard. It cost about £100 but is so much more convenient than climbing the loft ladder. We used it twice over Christmas so it was worth it.

I had to go up into our loft recently to add to the water pressure. I find I only have to do it annually and I always look on YouTube ,I simply add the name and model of my boiler and lots of simple videos come up to remind me which taps to move.
God bless YouTube I say.
Btw I do have an annual boiler service done by an approved heating engineer.
I agree with the original post though, it does seem to drop overnight, working fine one day,gone down the next day !!!

We have had combi boilers for 25 years and never come across this problem. We have 2 boilers and have had them both replaced so my experience is based on 4 boilers of this type.

Which make of boiler are they Monica, because next time we replace it I shall remember the name? Thanks.

We had a Valiant Combi boiler fitted last year. Very occasionally the pressure drops and it fails to come on in a morning. You just have to turn the taps located under the boiler for a few seconds to sort the pressure out. As it’s located on the landing in the airing cupboard it’s not a massive issue. I think it is a common problem and is more to do with the general water pressure in the area. The new boiler has been much more economical though so pleased about that with the recent increases in gas prices.

They have all been Worcester Bosch, although the current 2 are British Gas badged.

I am not saying we haven't had problems with them, just not this one.

Often the cause of a drop in water pressure is a leak.

We have a Worcester Bosch and at the last service, the engineer discovered a tiny leak in a valve, hence the reason for the drop in pressure we were experiencing
.
It has happened again over New Year, so we organised an engineer to come out. Not a big problem, the heating still works, we just keep an eye on the pressure and top up if necessary.

Reading through this thread I noticed how cold it had gone.
I checked the radiators - all cold. Checked the boiler and the pressure had dropped and turned off.
This hasn't happened for over 3 years. Strange that this thread appeared and my boiler stopped working.

The power of Gransnet!

Possible causes- you could have a tiny leak somehere you haven't seen. You can buy stuff you put in which seals these.
You may have air in the system- have you bled your radiators?
Your system may need cleaning there is stuff you put in the system which does this (think it's magnetic or something)
My DSs have done all of these for me at different times.

This happened to our daughter in a new build. We thought someone may have accidentally damaged a water main, as they were told this happens in combi boilers when the water pressure drops. They did something to get it working again, but don’t think it was adding water....more the twiddling of knobs! I got the feeling, from what she said, that this is a common ongoing sort of problem with this type of boiler.

Glad we stuck to our hot water tank, and emersion if there’s a problem with the boiler.

Is this progress? Boilers that keep needing a drink to stay on.
My old boiler just kept going with minimal attention.