Heating/Boiler/?Expansion vessel advice please.

[Wingedharpy]

Grateful for any advice here.

Combi boiler firing up and central heating and hot water warming well - but - within 20 minutes or so, of putting heating on, pressure in boiler goes up from 1.0 to 3.0 and rising (was at approx 3.75 when first noted).

Using hot water alone does not result in this problem, as far as I'm aware.

I have a boiler engineer coming to look at it but unfortunately, due to workload, he won't be here for another 9 days.

In the meantime am I better to:

1. Don't use the central heating at all (though it is bloody freezing, I have 2 electric heaters I could use).
2. Put the heating on to take chill off the house, but turn it off again when pressure above 2.5 - and repeat or
3. Run the heating as you want and take a chance the boiler will be salvageable by the time the engineer comes.

I didn't speak to the engineer when I booked him. I dealt with the receptionist.

It's a fine line between preventing hypothermia, preventing damp (old Edwardian terraced house, high ceilings, bloody cold), maintaining supply of hot water (vital), and preferably not turning a potential fixable problem into a condemned boiler problem.

Thank you.

Oh, our last boiler started doing this.
I kept bleeding the radiator nearest it to get the pressure down, which would work temporarily, but I did have to get an engineer out.
Can’t remember what the immediate solution was but eventually we got a new boiler (because the old one kept having different problems) and given the current weather that is a relief!
Pressure used to drop regularly too, at other times, and we never found out why, but subsequently an old radiator started leaking noticeably and getting that valve fixed seemed to solve the problem so it might have had a minute leak all the time.
Is there any way you can get someone sooner?

We needed an expansion vessel in our house which did the trick. The only issue is that they will have to the drain the system to insert it which can be time consuming, also they are quite big things. We had an expansion vessel already in place with our very old boiler; when we got a new boiler we removed it and then had to put a new one in afterwards- the size of our system clearly needs it.
If this is a new issue there may be an issue with your current boiler.
In the mean time, see if you can reduce the temperature of the system water ( the temp of the radiators) as it may reduce the volume expansion and hence the pressure. Usually a number dial in the boiler- ours goes up to number 6. Will take longer to heat the house or may just take the chill off.
worth a try?

Thank you.
My concern about bleeding the radiators is that the handbook says "normal operating pressure between 1.0 and 2.5".
It currently sits at just about 1.0 when boiler cool so, would bleeding radiators not make pressure too low?

Sounds like expansion vessel is full of water/out of air.
My simplest advice would be to turn the dial for the radiator water temperature down as low as possible and put the heating on constant 24/7. Assuming your house doesn't get too hot
Basically if you can keep it at constant temperature it will do less damage.

The advanced solution is to either pump up the vessel following the right technique or partly drain the system to let some air into the highest radiator eg towel rail but having the bleed valve on it open. Then close the bleed valve. Then it will act as a makeshift expansion Vessel.
But you would need a bit of know-how for either of those.

For the record, the damage would be to the pressure relief valve mostly, so not a massive disaster.

Thank you for you input - truly appreciated.

Particular thanks to @AppleTreeOwner as, following your post at 16.14hrs, I tried the turning down of the water temperature system and it appears to have worked!

Normal service appears to have resumed.

I am so, so grateful.
I'm warm for the first time in days and not fretting about what damage I'm doing by having it on.

I suspect that there's nothing wrong with anything and that the issue was caused by me tinkering about in an effort to "save energy", when I don't know what I'm doing!

In my defence, central heating and boiler was my DH's domain but he died earlier this year so I'm just doing my best.😢

Thank you all once again.

To save energy you need the system temperature on as low as possible for the weather conditions.
For instance in spring and autumn it could be as low as 40-50c and in winter like now it would be 60-70c.
Based on your comments about it being warm enough despite a low temperature I would guess you have a system sized for efficiency which means it would be designed to work at the lower end of the scale with large radiators. However that means if you set it to the higher end you'll get the problems mentioned. Boilers usually go up to roughly 85c which would be too much on any efficient system
Good luck!

Thank you @johnd2 .
That makes sense.
I blame Martin Lewis!