Rising boiler pressure

Question

When my heating is on the pressure in my Valiant boiler rises to just over 2 Bar from just over 1. Is this normal? The boiler also occasionally cuts out when the heating is on. Is this normal or a simple repair or will it need new parts? Thanks.

Mark · Accepted Answer

It is very normal for the pressure to rise. In terms of the boiler cutting out do you mean it the flame turn off? Or the boiler as a whole cuts out. Boiler make the heating reach the require temp and then the pump should stay on for a period of time until the temp drops and require more heat. But if it’s cutting out on a warning for example then there is an issue. If it’s high pressure then could be issue with expansion vessel. 
But few question 
How often do you top the pressure up 
When cold is pressure around 1 bar to 1.5 bar. 
And would need to more about “cuts out” this could be doing what it should be or could be an issue, need more info

Chas · Answer

As the boiler heats up pressure will rise. Try and bleed the radiators

Chris · Answer

Your boiler will probably need a new pressure vessel and pressure relief valve 
To supply and fit will cost £450.00
Would need to know the model number all information can be found on the data badge underneath the boiler. I could then advise you to have it repaired or install a new unit 
Thanks Chris

Graham · Answer

Yes this is perfectly normal. Water when heated expands by 4%. Inside the boiler there is an expansion vessel to allow the expansion and contraction as the boiler works. The pressure should be set to allow this expansion. There is a PRV (a Safety feature) that activates at 3.5 bar to protect the boiler. But a rise from 1 to 2 bar under heat is perfectly normal

Muhammad · Answer

Hi, your boiler might need the expansion vessel recharging if it is flat but if is internally damaged then you will have to get it replaced.
Regards 
Muhammad Afzaal

Stephen · Answer

There are issues with the expansion of the heating water. You should contact a heating engineer to fix. Its pretty simple for any experienced engineer

Ben · Answer

Possibly just the expansion vessel inside the boiler needing recharging but requires a gas safe registered engineer to do this

Neil · Answer

hi, yes this is normal as when the water in system heats up it expands,then contracts when cools down, so pressure will move up and down a bit thats totally normal.

The boiler will cut out when it has reached the temperature its set at, then come on again once the temp drops a bit and so on to keep it at the right temp, if that makes sense?

Martin · Answer

Hi 
Your boiler needs to have a hands on fault finding inspection done.
There are many variables as to why you're getting the symptoms you are.

John · Answer

Could be a blockage or the boiler may just need a good service.

Lee · Answer

Hi Harry, 
Its perfectly normal for the pressure to fluctuate during heating on a pressurised system.
The pressure shouldn't really go above 2b but as long as it remains below 3b its perfectly safe.
Depending how long you have the heating on, how quick the pressure rises and how big your property is, the expansion vessel could possibly do with pumping up, I'd suggest a full boiler service and advise the engineer you'd like the expansion vessel charged.

I hope this helps.
Lee
GWE Compliance

Ali · Answer

Rising temperature by 0.5 bar when heating is on is normal but according to your explanation, your system needs to be checked by a qualified heating engineer. It seems to have a problem in the expansion vessel or blocked pipework.

Gary · Answer

When boiler is in demand mode and is heating central heating makes bar pressure rise at least 0.5 bar as water expands when heated..you may be having an issue with expansion vessels. Not a problem at moment but get it checked it may need recharging(pressurising) before it becomes an issue. Boiler switching off occasionally is normal as boiler reaches temperature..it will then cool a bit and switch itself back on nothing to worry about.

Asim · Answer

Could be faulty expansion vessel or sometimes the expansion vessel needs recharging and the problem is sorted.  Also check the prv if water is dripping outside. that might need replacement.

Robert · Answer

Possible expansion vessel issue, would either need recharging or replacing.

Wayne · Answer

Hi there it sounds like a heat exchanger blockage or a vessel issue. Thanks, Wayne Boilerfixers

Rising boiler pressure

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