Wildly fluctuating pressure gauge - boiler

[Resident]

Hello,
When we turned the heating on for the cold season, the pressure gauge on the boiler has started to fluctuate wildly. The pressure when the boiler is idle seems to be falling rather quickly. Sometimes it has been down to 0.1 bar, but when the room heating starts it goes up significantly. When we re-pressurise the idle boiler to 1.2 bar (recommended), the pressure gauge skyrockets to 3.5 bars after the heating has been on for 10-15 minutes. When the boiler stops the pressure slowly goes down.

After re-pressuring the boiler to 1.2 bars, the low “idle pressure” slowly drops and in less than a week it is down to 0.3 bars, and we have to repeat the re-pressuring.

Background: The recommended pressure is 1.2 bar and the green range is 0.7 – 2.7 bar. Under 0.7 bar and above 2.7 bar the gauge is marked with red. Our combination boiler has had a leaking plate heat exchange that resulted in falling pressure. We had to re-pressurise the boiler once a week until we had it replaced this summer. The pressure gauge continued to drop very slowly after this repair of the boiler. This was a minor problem. We have checked all radiators for leaks and did not find anything. The boiler is an eight year old Worchester, Greenstar 28i Junior.

What could be the problem?

 

[leakydave]

First thing is to check the charge in the expansion vessel if you can... or get someone who is qualified to do so for you. I bet it has either lost its charge or the diaphragm is broken.

 

[Resident]

Thanks. But what will happen if this is left without being fixed? Will the constant re-pressurising add more and more hard mains water to the system that eventually will create too much limescale that cloggs the boiler?

 

[mcmoby69]

you need to read FAQ's

 

[muggles]

Thanks. But what will happen if this is left without being fixed? Will the constant re-pressurising add more and more hard mains water to the system that eventually will create too much limescale that cloggs the boiler?

Not limescale, but fresh water will cause corrosion in the system, resulting in all manner of expensive problems. The overpressure also puts unnecessary stress on your system components