I’m looking for some advice on a problem I have with the hot water system. I’m not too au fait with boilers etc, so as simple as possible please 
Boiler is an Ideal Classic FF260
Open vent system (Storage tank in airing cupboard, 2 open tanks in loft space)
For the last year after the hot water alone has been on for 10 minutes or longer, the pipes above the boiler begin to clunk, eventually this causes all pipework in the loft space to clunk resulting in warm/hot water being vented from the overflow. If the heating is on at the same time, this happens much less often (as it has been winter the heating has been on regularly, but as summer approaches I will want to turn off the heating). If the heating is on alone (no hot water) then there is no problem whatsoever, it has been on 24 hours at times. An engineer visited last year, didn’t seem to know what the problem was and said the following
1) Run the boiler at setting 4 ( of 6)
2) Run the Pump at highest setting (of 3)
3) Run Central Heating for 10 minutes before hot water (minimal success with this as water still eventually vents)
4) Power Flush the system
From what I have read about Power Flushes this seems to be primarily cleaning radiators and improving heating. As the central heating seems fine, radiators warm evenly, I’m uncertain what benefit this will give and don’t want to spend money and be no nearer fixing the real issue.
Any advice on what maybe causing the problem would be much appreciated, and also advise on whether a power flush would resolve the problem.
Thank You
Boiler is an Ideal Classic FF260
Open vent system (Storage tank in airing cupboard, 2 open tanks in loft space)
For the last year after the hot water alone has been on for 10 minutes or longer, the pipes above the boiler begin to clunk, eventually this causes all pipework in the loft space to clunk resulting in warm/hot water being vented from the overflow. If the heating is on at the same time, this happens much less often (as it has been winter the heating has been on regularly, but as summer approaches I will want to turn off the heating). If the heating is on alone (no hot water) then there is no problem whatsoever, it has been on 24 hours at times. An engineer visited last year, didn’t seem to know what the problem was and said the following
1) Run the boiler at setting 4 ( of 6)
2) Run the Pump at highest setting (of 3)
3) Run Central Heating for 10 minutes before hot water (minimal success with this as water still eventually vents)
4) Power Flush the system
From what I have read about Power Flushes this seems to be primarily cleaning radiators and improving heating. As the central heating seems fine, radiators warm evenly, I’m uncertain what benefit this will give and don’t want to spend money and be no nearer fixing the real issue.
Any advice on what maybe causing the problem would be much appreciated, and also advise on whether a power flush would resolve the problem.
Thank You
