Combi system.One radiator getting air in

[whatsthenews]

New Combi system (boiler and microbore re-pipe)about a year old. All radiators have TRV's apart from one of the bathrooms
Started noticing a single loud bang,possibly from the hall radiator shortly after radiators have gone off.
I say possibly because the radiator in the room above the hall keeps getting air in it and needs bleeding, so it could be coming from this one, but it doesn't sound like it.
Difficult to know how long it's taking for air to stop it working properly because it's a room we only use occasionally and it's not until one of us goes in in and realises it's a bit nippy that we check and bleed it, plus have hardly had heating on over the last couple of months.
Whilst we can bleed the radiator and solve the immediate issue, is there anything else we can do to try and work out why/where air is getting into the system? The boiler pressure isn't dropping except slightly after we bleed the radiator and no signs of any leaking radiators.
We had the downstairs rooms replastered after the system was fitted and the plasterer took the rad's off the walls and laid them on a variety of tool boxes etc while he was plastering. Is it worth checking that the valves are all tight?
Thanks in advance

 

[John.g]

Can you set the HW SP temp to its max or ~ 60C and open a hot tap only and see if the boiler runs "normally" at this temp for 5 minutes or so, then change back to CH but leave the HW SP at 60C and CH SP at 70C and watch the temperature rise again before the boiler cuts out. The first test IMO should prove that the circ pump is OK and if the boiler continues to cut out after 20 secs or so on CH then it may point to some problem with the circulation around the radiator system or a boiler problem.

 

[whatsthenews]

Can you set the HW SP temp to its max or ~ 60C and open a hot tap only and see if the boiler runs "normally" at this temp for 5 minutes or so, then change back to CH but leave the HW SP at 60C and CH SP at 70C and watch the temperature rise again before the boiler cuts out. The first test IMO should prove that the circ pump is OK and if the boiler continues to cut out after 20 secs or so on CH then it may point to some problem with the circulation around the radiator system or a boiler problem.

Hi, sorry for late reply. Thanks will do so. Just to say- I turned the HW SP up to about 56 yesterday.
It was playing silly buggers earlier today. The "heating" light (as opposed to HW light) is lit. Again, the rad in hall was barely hot, but took the TRV off and it was jammed.
Sorted that and turned the stat up to 22c (actual room temp' was 20c) heating came on and rad' was red hot within 4-5 mins.
Thought I'd solved the issue but it's still doing it, but boiler water temp now goes up to 56c (the HW SP) then cuts off.
Does the boiler "act" differently depending on the difference between the actual and set room temp?
[automerge]1601065843[/automerge]

Hi, sorry for late reply. Thanks will do so. Just to say- I turned the HW SP up to about 56 yesterday.
It was playing silly buggers earlier today. The "heating" light (as opposed to HW light) is lit. Again, the rad in hall was barely hot, but took the TRV off and it was jammed.
Sorted that and turned the stat up to 22c (actual room temp' was 20c) heating came on and rad' was red hot within 4-5 mins.
Thought I'd solved the issue but it's still doing it, but boiler water temp now goes up to 56c (the HW SP) then cuts off.
Does the boiler "act" differently depending on the difference between the actual and set room temp?

Just wanted to say that the hall radiator was hot first thing this am when heating came on on auto, but maybe it was jammed on 3? Does that make sense?
[automerge]1601066837[/automerge]

Hi, sorry for late reply. Thanks will do so. Just to say- I turned the HW SP up to about 56 yesterday.
It was playing silly buggers earlier today. The "heating" light (as opposed to HW light) is lit. Again, the rad in hall was barely hot, but took the TRV off and it was jammed.
Sorted that and turned the stat up to 22c (actual room temp' was 20c) heating came on and rad' was red hot within 4-5 mins.
Thought I'd solved the issue but it's still doing it, but boiler water temp now goes up to 56c (the HW SP) then cuts off.
Does the boiler "act" differently depending on the difference between the actual and set room temp?
[automerge]1601065843[/automerge]

Just wanted to say that the hall radiator was hot first thing this am when heating came on on auto, but maybe it was jammed on 3? Does that make sense?

Ran HW with HW SP at 60c and the boiler temp reaches 60c and stays there. Then (with room stat turned up to 22c, actual room temp 20.5) boiler temp didn't go above 60c, BUT it didn't cut out when it reached 60c either.

 

[John.g]

"Ran HW with HW SP at 60c and the boiler temp reaches 60c and stays there. Then (with room stat turned up to 22c, actual room temp 20.5) boiler temp didn't go above 60c, BUT it didn't cut out when it reached 60c either."

Is the CH SP still set to its original 70C?, if so, then when room stat requests heat the boiler should ramp up to 70C and once it reaches this SP temperature the boiler will simply modulate down to maintain this 70C until the room stat is satisfied which will then cut out the boiler, if its maintaining the HW SP of 60C, then this is incorrect IMO. While its running on CH at 60C can you reduce the HW SP from 60C to say 45/50C and see if the boiler cuts out or reduces to this temperature, this would confirm that it is using the HW SP for both hot water and heating as appears to be the case.

 

[whatsthenews]

"Ran HW with HW SP at 60c and the boiler temp reaches 60c and stays there. Then (with room stat turned up to 22c, actual room temp 20.5) boiler temp didn't go above 60c, BUT it didn't cut out when it reached 60c either."

Is the CH SP still set to its original 70C?, if so, then when room stat requests heat the boiler should ramp up to 70C and once it reaches this SP temperature the boiler will simply modulate down to maintain this 70C until the room stat is satisfied which will then cut out the boiler, if its maintaining the HW SP of 60C, then this is incorrect IMO. While its running on CH at 60C can you reduce the HW SP from 60C to say 45/50C and see if the boiler cuts out or reduces to this temperature, this would confirm that it is using the HW SP for both hot water and heating as appears to be the case.

It didn't yesterday with CH SP set at 70c, but this evening it's going up to 60c pretty rapidly (with HW SP at 60c) ,then gradually going up to about 65c. If I turn the HW SP down to 40c with heating running the boiler temp doesn't drop to 40c. Maybe it's just modulating or it's got something to do with it being a condensing boiler?
Anyway, engineer seemed to think it was fine. Only a few iron filings in the magnetic filter which he said is normal for the system being about a year old.