Persistant air in Microbore system

[Darden]

Hi,
Bearing in mind that I am a novice in these matters I wondered if someone could be so kind as to give their oppinion on the following problem;

As far as I understand I have a gravity fed hot water system and a pumped central heating system. The boiler is a "Baxi Bermuda 5174E back boiler feeding to radiators through a microbore system. I am led to believe that there will be a manifold somewhere but I'm damned if I can find it! The problem is (and always has been in the 3 years I have lived in the property) air in the system that I am unable to bleed out through the rads. At times I can hear air in the back boiler when the CH is off but hot water is being called for. I have had the pump changed and this made a degree of improvement as far as the noise is concerned but there is still an obviously large degree of air in the system somewhere.

Is there a bleed valve on the mysterious manifold (any ideas where it could be?) or am I missing some other option?

Any help/suggestions would be gratefully received!!

 

[namsag]

There is not normally a bleed screw on manifold...You should always bleed your system with the heating off or it could such air in if the pump is running .
Noise from boiler does it start after just the water has been on for half an hour ish. it could be the boiler stat has gone and it is getting too hot this can also cause air in a system

 

[gas4you]

Commonly on this type of gravity system the pump would be installed on the return and 'sucking' the water through it, hence why you should heed namsag's advice regarding when to bleed your rads.

Would also be worth checking your f&e tank is full of water.

 

[Darden]

Thanks for your advice Namsag and Dave,

I'm aware that the system should only be bled when the heating is off and have done so several times so pretty sure thats not the cause of air getting in.

Have checked the F&E tank and it seems to be fine (half full?).

As regards the thermostat having gone, I assume the boiler would continually overheat and would disgorge steam through the vent pipe (?) into the F&E tank. If thats the case and there is no steam, does that suggest the thermostat is ok? Failing that how else could I check?

Thanks again lads, your advice is really appreciated.

Alan

 

[gas4you]

Could be a blockage in the cold feed to the system, and what you think is just air could be caused by a lack of water in the system.

 

[Darden]

Thanks Dave, this may be a silly question but how would I check?

 

[gas4you]

Connect a hose to a rad drain off and drain water out. If there is no blockage then you will see/hear f&e tank filling up.

If it doesn't fill, or the level in it doesn't drop, then you have a blockage.

 

[Darden]

Ah yes, that would be logical !

Thanks again Dave.