combi high pressure after start up

[2cautious]

I have a halstead finest gold combi--about 9 yrs. old. When the central heating starts up , all is ok. pressure is 0.5 and gradually increases to 3+ when I turn it off and wait for pressure to drop to about 1.5 ish and then turn it on again. It then continues ok until 3+ is reached and I turn it off and repeat the above another 2/3 times until it turns itself off at say 2.5. It then continues to function "properly" (no high pressure ) and after each heating "sequence" the max pressure reached reduces down to 1.5 ish and then the boiler works ok all evening / day.
Do you think that the central heating thermistor is at fault? (expansion vessel pressure is 15 psi and there is no air in radiators )

Thank you
2

 

[powell30]

No.

Expansion vessel is duff or you have a blockage (filter maybe?) that is causing pressure to rise. Thermistor or overheat stat will cut in and shut down boiler if it was a heat issue......my money is on your expansion vessel

 

[gas4you]

See FAQ's on how to check your expansion vessel.

 

[2cautious]

Powell30-Gas4you
Thank you for your help, I think the "flexy" pipe from ex. vessel is blocked.( put water pressure to 0.5 bar , ex.v. pressure to 0.5 bar-- then increased water to 2.5 bar and ex. v. pressure did not move, stayed at 0.5 bar ) so by my logic , pipe is blocked, do you knowledgeable people agree? ( i`ve "fondled" the pipe--bent it and re-bent it to move sludge, but no success)
If so, how do I clean / replace this pipe, as it seems impossible to get a spanner near it other than removing most of the boiler ( its at back of boiler)
Would a drain-down and clean with "anti- sludge" do the trick?--I intend living here for next 10--20 yrs.

Thanks

2

 

[gas_man_gaz]

did you check the pressure in the exspansion vessel wen the system was empty? i have had it once before where the hose has been blocked, if it is id guess it will be blocked at the end where it enters the system. u'll need to drain the sys undo the end and poke a bit of wire through it to clear the blockage.. wa a nightmare wen i did it!