Air in System - Could it be a scaled up Oil Boiler?

[ploughback]

I have a Myson oil boiler supplying 8 rads but am getting continually air in the system. A couple of plumbers have checked out the pipework, fittings and design (all OK) and I have also had a new thermostat fitted on the boiler but I still have the problem.

Only clue is that air does not seem to be drawn in/produced when boiler is on a lower setting (4 or below) but does on anything higher. I do have most of the TRVs turned down low but presumably the lower call for heat should be acnowledged by the thermostat.

Only other thing I can think of is a scaled up boiler producing hotspots and boiling up water above certain thermo settings.

Any ideas would be appreciated.

Tom

 

[jobloggs]

Is it air or is it hydrogen gas from corrosion? Inhibitor in system?

 

[cozzmic]

Sounds like it's corroding up and the air is actually hydrogen gas. If you have a air cock which is pointing away from anything flamable on your rad, open it and hold a lit match next to it. If it lights blow it out shut the aircock and your system needs cleaned out and inhibitor added. But may need to trace why the system is doing it. By the way you'll get a lovely blue flame out of the rad and if you quick might be able to do some silver soldering. (just joking).
ps is the system sealed, got an expansion vessel?

 

[jobloggs]

Is it air or is it hydrogen gas from corrosion? Inhibitor in system?

 

[oilman]

Is there an echo in here?

 

[ploughback]

Cozmic/Jobloggs

Nice one, thanks for the tips. Just moved into house so it could be corrosion due to no inhibitor however Ive had all the rads off (very little sludge) and chemical flushed/drained & filled a couple of times and there was very little sign of any probs in the water. Always seems to produce the same volume of gas for a given time of boiler operation which made me assume air.

I will crank up the heating and try and light the off-gas and report back...

Cheers

 

[jobloggs]

Reply suggests that you didn't replace inhibitor when you refilled after flushing. Lack of sludge suggests that you had inhibitor before.

However it is not quite clear whether you had the problem before you did all the workon rads and flushing.

 

[ploughback]

When I refilled I put in inhibitor but not sure what the situation was before I had the problem. When I moved in I replaced all locksheilds & TRVs as a couple were slightly leaking and the rest were battered or covered in paint. Ive since run the heating the whole winter and keep getting the air problem.

 

[ploughback]

Just tested the gas - no blue flame so it must be air.

Cozzic - re your earlier question - it is a open vented system. (Boiler is a good 12 years old).

 

[jobloggs]

Just a thought. When the system is all warmed up feel the water in the F&E tank in the roofspace. It should be cold. Check the water level in it and the operation of the ballcock when you are at it.

 

[ploughback]

Just been up there and the water is stone cold, level is normal (well above outlet) and ball-cock operates fine.

About 3 months ago I tied up the ballcock to test water level (primarily to flag up any leaks which might let air in) and the water level remained constant (albeit for maybe a cupfull loss which I put down to evaporation). Ball cock is now allowed to operate normally.

 

[jobloggs]

Just trying to eliminate possibilities.

I have seen some suggestions that air can be sucked in through micro leaks in pipework on the suction side of the pump. I can't see how this could happen unless all radiators were shut off, the HW was shut off by a motorised valve and the feed and vent were on the pressure side of the pump.

What controls have you? room stat, tank stat, motorised valves?
What is the vent/feed pipe arrangement?

 

[ploughback]

This is probably where I get out my depth!

Room stat in hall (set high - I dont use this to control boiler and rely on TRVs to regulate heat in rooms). Seems to work fine when I turn it down and it clicks off heating.

TVRs are on all rads except lounge which runs at full heat. Therefore presumably boiler cycles on and off based on boiler stat control - presumably kicking back in when it sees the return flow dipping below set level.

Motorised valve? - Do you mean the valve above the pump which sends to either water or heat - yep got one of those. Also stat on copper tank - Currently set at 55 and clicking on off OK.

Vent pipe feeds into open heating tank - about 4 inches above water level. Pup on min speed so if its sucking in in would have to be near pump - no sign of any probs there.

Interstingly I never get any air in the water side but I have put this down to the fact that the boiler is never on long enough or run hot enough to produce air problem where on the heat side the problem occurs after approx 45 mins running and you can start to hear air moving through the system

 

[jobloggs]

You have the basis of a fully controlled system but seem to be operating it somewhat unconventionally.

You should have the room stat where there is no TRV and set the stat at 20 degrees or so. Could get away, I suppose, by turning hall TRV fully open and stat down to a level where it will operate. You should have TRV in the living room.

Alternatively you could move stat into living room. Is in on a dividing wall? and leave all TRVs as is.

Yours is a Y or W plan depending on type of 3 port valve.

As your system is set up now the room stat is never satisfied. Your pump is being controlled by the Timer and runs all the time that is on. Your boiler is operating on its own thermostat. You are not getting the benefit of all the expensive bits and pieces in your system, overworking the pump and not controlling the heat in your L'room very efficiently.

Have a look at:

http://www.pegler.co.uk/training/index2.html

Where do vent and feed connect into HW and or CH circuits?

 

[ploughback]

Room stat in hall is on adjoining wall to lounge so I could easily move room stat into lounge. (Room stat and rad without TVR then would both in lounge from where i could control temp and rest of rads controlled by TVR.

Alternately presume I could take TVR head off hall rad and leave room stat where it is in hall? Prob best if I go with both in lounge as this is main living room in winter. Any rules about stat being not being near a wall uplighter fitting? Would probably be only a meter and a half from rad too...

Not sure of feed/expansion set up - I will check your link and see what it might look like..

Agree would make system more efficient - could it have a bearing on my air prob?

Been reading about kettleing - does the boiling effect (regardless of how it is caused) force air out of the and cause it to gather in pockets? i.e. like you see air bubbles forced out of water in aboiling kettle or pan...