How to remove air from direct heating system

[Baldric]

I have a Rayburn oven with a back boiler gravity heating water to a direct hot water cylinder. The Rayburn had been overheating and therefore I added a heat leak towel radiator.
My problem is that the hot feed pipe to the towel rail is constantly air locking and will ony work for a few hours after air removal before locking again. I guess this is the dissolved air constantly being introduced by new mains water entering the direct system when in use. I assume the hot feed to the towel rail locks because the dissolved air is converted during the heating process to form pockets of air that lock in my pipework.
Can anyone offer any advice on how to trap and remove this air either at the cold water tank and/or elsewhere in the system and thus avoid my ongoing air locking issue.
Any help would be appreciated.

 

[djboyd]

Baldric, what is "dissolved air" - is it different to normal air?! also, your system you say is direct and you mention mains water - surely if you are using a back boiler (as i am) then it is a vented and gravity fed system. if air is a problem, perhaps an auto air vent at the highest point would solve your problem. you might not get a lot of info with back boilers on this site - we are in a minority!

 

[Baldric]

djboyd, Thanks for your reply. "disolved air" I guess does not truly exist, what I mean is the very small air bubbles that are present and fluid within the mains water supply. Mine is a vented gravity fed system but as it is a direct cylinder, new mains fed water is continually entering the heating circuit. My understanding is that the small air bubbles in mains water can travel throughout the system and only change their state (to form large air pockets) when heated. Normally, these air pockets pass through the large pipes to the hot water cylinder and vent harmlessly. In my case, probably through poor plumbing design, the air pockets enter the hot feed to the towel rail and air lock. Rather than extensively modify the plumbing, I was hoping for a simpler solution. Perhaps a auto air vent on the output of the boiler around 1mtr away on a near 90d bend would do it, but, I am not totally sure this will work hence my asking for advice. Thanks.

 

[djboyd]

Surely your direct cylinder is fed from a header tank and not mains pressure? This would be safer, mains pressure / unvented cylinder with direct doesn't sound right to me. Do you not have a header tank above the cylinder? if so, no air should be able to enter from the water supply.

 

[Baldric]

Yes my cylinder is fed from a cold water storage tank and is vented. The problem is that the constant flow of mains supplied water (fed via the tank) introduces miniature air bubbles that can travel down the pipes and into the heating circuit which, when heated, can combine to form large pockets of air in the system.

 

[djboyd]

Yes, I now picture your system! perhaps the supply of water drains the header tank faster than it can refill and introduces air?

 

[Baldric]

I have already checked the level of the cold water storage tank during full demand and the level is maintained at an inch or so below the ballcock shut off point and comfortably above the tank outlets.

 

[justlead1]

Hi Wht not run the pipe work so as it rises towards the rad?

 

[Baldric]

The pipe work does rise towards the rad (just) but the force of the gravity is not enough to push any air past the tee from the hot feed pipe. Even if the air made it into the rad, the amount of air being constantly generated would fill the rad in no time.

 

[justlead1]

I do not want to disappoint you but air is likly to being drawn in to he system, rather than being in suspension. I would be looking at the system design,pipe sizing etc. In order to solve the problem.

 

[djboyd]

Baldric, if you have a header tank full of water, which remains full of water at demand, then it cannot be the source of the air. any air introduced by mains water will obviously rise to the top of the tank. Your system must be being supplied with air free water and the problem air is being drawn in somewhere else.

 

[tiling spread]

YouTube - toms top tip how to shift an air lock part 2
YouTube - toms top tips how to move an airlock
sorted

 

[Baldric]

Thanks for all your replies. Problem now resolved. It was micro-air in suspension within the mains water supply entering via the cold water tank circulating around the system and being released by the heat from the boiler. This air then blocked the radiator feed pipe first, before naturally venting through the hot water cylinder/vent. Simply fitted a 28mm tower air separator before the rad take off, venting also to the tank, and problem solved.

 

[djboyd]

'It was micro-air in suspension'

Is this a wind up? or are you some kind of boffin?

 

[Baldric]

No wind up and no boffin either. Probably just not using the right words but hopefully you get what I mean.

 

[oilman]

pressurised water contains air, try taking a glass of water from the kitchen tap and watch the bubbles. The air is what makes Tea work.
Boiling of water also creates bubbles, if your rayburn is overheating it will make bubbles which need to be vented

 

[djboyd]

Baldric, I get what you mean! I have my own air problems with my system too. Glad it is sorted, good forum don't you think?