Cutting out and pressure problem

[dogtooth]

Hi Everyone. I have an Ariston Genus 27MFFI combi.The problem is that it is cutting out activating the shutoff LED. And continues to cut out even after the reset button is pressed. Once the boiler is cold it will work again. The pressure gauge falls to about 0.4 and will slowly rise to 1.8 (takes about 14 mins)and then cut out again.This coincides with a rapid ticking noise coming from the boiler. Whilst it is heating it will switch the primary heat exchanger off and then back on when temp is reached, the pump still circulates the water. When it cuts out the pressure needle jumps a bit and again when reset. There is no water coming from the emergency safety valve, pipe covered in cobwebs and bone dry. There are no visible leaks in the heating system but I haven't been under the floor boards yet! I normally have to top up the system once a month by about 0.5 bar.
The hot water will work, unless the heating has just cut out (accompanied by the ticking noise again). In this case the boiler needs to cool down (when the pressure has dropped?). Things seem to stop after the ticking noise starts?
This part may have no relevance but I will mention it anyway. I have been decorating two weeks ago and removed a radiator and replaced it when finished (no leaks). The unusual thing was that when I went to top up the system the water pressure coming to the house was very low due to a burst water main locally. The pressure was not enough so I had to wait to top up until they had fixed the main.Then there seemed to be no problems. When the system has cooled down it works again until the pressure rises to about 1.8bar.
Sorry for the long post but didn't want to miss anything that may be relevant.
Any help or ideas would be gratefully recieved. I was thinking it could be a fault with the expansion vessel from reading other posts.
Thanks.

 

[Whiter]

I am not familiar with this boiler. But have you checked the pressure in the expansion vessel, this could account for the movement in the pressure gauge. Are your radiators getting hot, could be that the boiler is overheating(reset button?) and cutting out thus accounting for the pressure rise, boiler then resets when cooled down, this could be caused by a lot of different things, thermistors, PCB, gas valve, overheat stat etc. Does it cut out at all when running hot water? Could try looking in manual for faults, but it sound like you will need an engineer.

 

[dogtooth]

Thanks Whiter. the radiators heat up for about 15 mins then the boiler switches off until its cooled down then can be reset again for 15 mins. the hot water will work Ok if the heating has not been on, but cuts out if the heating has reached the 1.8 bar pressure or this could be overheating. If I turn off the heating the hot water is fine.I've checked manual for faults but nothing stands out. I will call an engineer on Monday.
I don't know how to check the pressure in the expansion vessel?
Thanks for your help, much appreciated.