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Plumberpro, Home Appliance Technician
Category: Appliance
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Experience:  Heating and hot water heating appliances experienced
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why does the pressure rise when i put my heating on then go

Resolved Question:

why does the pressure rise when i put my heating on then go back down if i knock it of
Submitted: 2 years ago.
Category: Appliance
Expert:  George-Allsorts replied 2 years ago.
George-Allsorts :

Hello, my name is***** be patient whilst awaiting any responses as I'm not constantly available.

When you put your heating on the water heats up and causes pressure to build.. when you turn it off, eventually the water cools and therefore the pressure decreases

Customer:

if i leave the heating for 5 minutes the pressure keeps rising into the danger zone so i have to knock it off

George-Allsorts :

what pressure does the gauge fall to when it is switched off?

Customer:

it falls slowly to 1 half bar after about 4 minutes

George-Allsorts :

How high is the pressure going up when you turn the boiler on? There is a pressure relief valve on all modern boilers that should kick in at some point

Customer:

it is going up to just over 3bar then i knock it ff

Customer:

the pressure only rises when the central heating is put on.the pressure is ok when you are just running the hot water

Expert:  Plumberpro replied 2 years ago.
Hi . the pressure goes up because when water heats it expands. In a sealed system , ie Combi/ system boiler, the expanded water is taken up in an expansion vessel. This is like a balloon within a metal casing. This balloon is pressurised by pumping it up with a pump( car tyre pump or bicycle pump) to 1.7 bar. .if this balloon goes flat the heated water has no where to expand against.the pressure then rises and if goes above 3 bar will empty out of the safety expansion valve. This then causes a cycle of repressurising, dumping out of the safety and so on. The only solution is to repressurise the vessel or if it has failed , replace it
Plumberpro, Home Appliance Technician
Category: Appliance
Satisfied Customers: 634
Experience: Heating and hot water heating appliances experienced
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Expert:  George-Allsorts replied 2 years ago.
Sorry my computer is just crashed. You have a faulty expansion vessel. You will need the services of a plumber to correct this

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