Rising boiler pressure

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.

Asked by Harry on 31st Mar 2020
Expert Trade Answers
"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"
Answered on 31st Mar 2020 - Member since Jan 2019 - report
"As the boiler heats up pressure will rise. Try and bleed the radiators"
Answered on 31st Mar 2020 - Member since Mar 2019 - report
"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"
Answered on 31st Mar 2020 - Member since Jan 2020 - report
"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"
Answered on 31st Mar 2020 - Member since Mar 2020 - report
"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.
Muhammad Afzaal"
Answered on 31st Mar 2020 - Member since Sep 2018 - report
"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"
Answered on 3rd Apr 2020 - Member since Dec 2016 - report
"Possibly just the expansion vessel inside the boiler needing recharging but requires a gas safe registered engineer to do this"
Answered on 31st Mar 2020 - Member since Apr 2019 - report
"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?"
Answered on 31st Mar 2020 - Member since Feb 2020 - report
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."
Answered on 31st Mar 2020 - Member since Mar 2020 - report
"Could be a blockage or the boiler may just need a good service."
Answered on 31st Mar 2020 - Member since Apr 2019 - report
"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.
GWE Compliance"
Answered on 31st Mar 2020 - Member since Mar 2020 - report
"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."
Answered on 9th Apr 2020 - Member since Oct 2019 - report
"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."
Answered on 1st Apr 2020 - Member since Jan 2015 - report
"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."
Answered on 31st Mar 2020 - Member since Feb 2020 - report
"Possible expansion vessel issue, would either need recharging or replacing."
Answered on 31st Mar 2020 - Member since May 2019 - report
"Hi there it sounds like a heat exchanger blockage or a vessel issue. Thanks, Wayne Boilerfixers"
Answered on 1st Apr 2020 - Member since Jan 2019 - report
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