Pressure low in CH but HW is ok

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[Advance warning - I'm not an expert so will try not to bandy around technical terms that I don't fully understand!]

Our central heating is going off occasionally for about a day at a time, and can go for weeks before it goes off again. It has gone off again now. The pressure gauge seems to fluctuating between about 0.8 and 1.2. I assume that the system just shuts off when the pressure is too low (below 1)?

A few times the boiler has been reset.

There is a screw valve below a flexible pipe leading up into the boiler (the filling valve is presume). Is it right to assume that by opening this valve, the incoming water should repressurise the system and force any air out? I don't sense that there is air in the system as there is no noise and the radiators work fine (and evenly) when the CHS is working.

The system is:
Potterton Prima F
Landis & Gyr switch
Grundfos pump

 

[AnonymousImport]

I have recently had a pressurized system installed & was advised to maintain pressure at 1bar, I was told that this pressure should only fall if there was a leak in the system. I had call to remove a rad, I lost pressure & opened the valve you refer to, which restored the pressure.

 

[IanDB]

When you pressurise the system you are not forcing air out, you are compressing the air in the expansion vessel. Without this air gap the hot water in the system would just expand and (as water does not compress) the pressure would increase until the Pressure Relief Valve opened (at 3 bar) and you get a puddle of water underneath your boiler.

If you are convinced that it is something to do with water pressure you could pressurise the system up to 1.2 bar and see if it makes a difference. However I would think this unlikely as I believe most systems will work down to 0.5 bar.

If your boiler is going into lock out it may be due to some other reason such as the gas burner not getting sufficient air to ignite in time. It may only need a service to ensure the burners are clean.