system wont re pressurise and constantly fire up on and off!

[jackpot]

I have a combi boiler which is a Glow worm swift flow that for a while has constantly lost pressure. I have had to top up the system every few days. It would only lose pressure after heating had been on.
All of a sudden it has regained its constant pressure and is on the 1.0 bar mark. It slightly goes up to around 1.3 when heating is on..i thought great but since this the system will not top up whatsoever. No water will enter the system....Why?
Also going back to the losing pressure days I noticed and still do when the hot water tap is on the system constantly clicks, and fires up on and off like someone is just turning the heating on and off constant.

Ideally a new boiler is needed but what can be the main problem be...pressure relief valve?
For the record no leaks have been found and no water is or has been coming out the outside overflow.

thanks guys

 

[plumbswe]

Pressure sensor

 

[jackpot]

Thanks. Any ideas where i can find this on the system and whether i can replace easily enough.

 

[peekay53]

well yes it would be very easy to tell you where pressure switch is but it would be much better if you got the gas safe registered engineer to show you when he replaces it and gives boiler long overdue service

peekay53