Combi Pressure and Noise

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I have a combi system,I have noticed that the
pressure drops to 0 when the system is switched off.When it is switched on the boiler is noisy and sounds like there is air
going through the boiler/pipes.Once the system is running the pressure returns to normal 2bar but then carries on climbing
until it is into the red on the gauge but then drops back to 2bar.When the system is
switched off it drops back to 0 within 15 min.I don't have any idea why this would do this,if there was a leak that drops the pressure to 0 how can it go back to normal and above without adding more water to get the pressure to normal.All the radiators heat up as normal and there are no cold spots,all
radiators are on the ground floor except one
in the loft conversion,the one in the loft runs off the standard system there are is no extra pump for the loft but this hgas been ok.We bought the house this way so any pointers or help would be much appreciated.
 
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Sounds like your expansion vessel in the boiler needs recharging.

Drain the system. Use a car tyre footpump to achieve 1 bar of air pressure via the vessel schrader valve.

Refill the system to 1.5 bar, bleed rads. check pressure is 1-1.2 bar cold. Refill as necessary.
 
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Is this the valve at the top of the combi?

Is the 1 bar the pressure in the expansion vessel and not the gauge on the system ie the gauge on the foot pump.

Which means the system gauge stays at 0 until I refill the system up to 1.5

 
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You didn't say which make/model of combi you had.

The valve is on the large red vessel, which is either visible below the burner assy, or at the rear of the boiler. You are looking for a car tyre style valve. The valve at the top of the boiler is probably the auto air vent.

You set the pressure to 1 bar AIR pressure in the vessel - on the tyre pump gauge NOT the boiler gauge.
 
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Thanks a lot,did it last night and it worked a treat.

Pressure is now back to normal and the noise has gone as well.

Big smiles all round :)

Thanks Again
 

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