Recurrent air

[gaj2002]

Hi, hoping for some help if anyone has any ideas

Sealed system, Ideal system boiler and big hot water cylinder, fitted three years ago

At the time of boiler installation (which accompanied an extension project) we had major problems with recurrent air causing airlocks; fitter had failed to identify that the cast iron radiators took us well over boiler system capacity so we needed an expansion vessel. Additional expansion vessel fitted (I think it's 25 litres), then a couple more rounds of bleeding and turning radiators off to clear airlocks, then we were ok for a couple of years.

Anyway we have had a new ground floor extension this time, a couple of new rads, changed a couple of existing to cast iron.

However we had one minor disaster along the way where (doesn't matter why) the pressure was turned up to 2.2 bar cold, then when the heating was run a few radiator valves burst; these have been replaced.

At the end of project two I feel like I'm back in the position I was in at the end of project one - recurrent air. I can bleed radiators (I know which ones catch the air) and I can restore the heat to one particular first floor bedroom by turning off all the ground floor rads and a few first floor ones... but a week later the airlock has returned.

Any suggestions very gratefully received

My current list of guesses:

- PRV
- Problem with boiler expansion vessel or additional expansion vessel
- I need yet another expansion vessel
- Dissolved air from the last round of work is really stubborn and I need a couple more rounds of bleeding etc to get rid of it (although I feel I've done enough rounds that I think this is unlikely)

I'm guessing a leak is unlikely as I don't seem to be losing pressure noticeably

Thanks everyone!

 

[footprints]

Strange if you are bleeding weekly you should be loosing pressure.
Are you sure the filling valve is fully off, its possible you have a leak under floor or the PRV is letting by. Constant air means water is changing or corrosion in the system creating Hydrogen gas.
Given the cast iron rads will corrode as soon as you fill the system (they should stop once all the oxygen is out o the filling water) lots of cast rads might mean lots of initial corrosion till it settles down.
Worth a look here it explains what can happen under the right (wrong !) conditions.

How to: diagnose the cause of circulation issues in central heating systems

My customer's central heating system has poor circulation About the problem If your customers are experiencing poor circulation in their homes, such as ineffective radiators, it could be caused by hydrogen in radiators and so it is important to accurately identify the cause of the issue in order...

sentinelprotects.com

 

[gaj2002]

Strange if you are bleeding weekly you should be loosing pressure.
Are you sure the filling valve is fully off, its possible you have a leak under floor or the PRV is letting by. Constant air means water is changing or corrosion in the system creating Hydrogen gas.
Given the cast iron rads will corrode as soon as you fill the system (they should stop once all the oxygen is out o the filling water) lots of cast rads might mean lots of initial corrosion till it settles down.
Worth a look here it explains what can happen under the right (wrong !) conditions.

How to: diagnose the cause of circulation issues in central heating systems

My customer's central heating system has poor circulation About the problem If your customers are experiencing poor circulation in their homes, such as ineffective radiators, it could be caused by hydrogen in radiators and so it is important to accurately identify the cause of the issue in order...

sentinelprotects.com

Sorry I imagine I do lose some pressure from the bleeding

But my point was otherwise I don’t seem to be noticeably losing pressure