Air lock in old gravity heating system ?? No hot water


Postby EverF » Tue Feb 03, 2009 10:50 am

Hi Everyone,

After trawling the net trying to find an answer I found this site which cam the closest with a previous post so I thought i'd try and get a bespoke answer for myself!

I have an old old boiler in my kitchen which heats the radiators and at the same time heats the water in a tank upstairs (there are no upstairs radiators) I recently had a problem with an old downstairs radiator which had rusted through at the bottom, after trying to turn off the valves and realising that they were both cream crackered I removed the radiator and blocked the pipe ends.

The hot water has been fine for a couple of weeks, then I noticed that one of the other radiators was only half hot, so bled it.........now no hot water..

I have bled all other radiators, but still nothing.....


I am guessing from other posts that there is an air lock in the coil. BUT I don't know which is which pipe on the tank? nor how to remove the air lock? Do I just crack one of the pipes open until water flows out? Which one?!!

Incidently, the boiler is located directly underneath the tank, neither of the 2 "large" pipes which go upward from the boiler are hot when the system is running.


Any help is appreciated so that I am armed with some info when I go home tonight with my spanner!

Cheers
Malc
EverF
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Postby EverF » Tue Feb 03, 2009 7:31 pm

Now that i'm back home and had another look I can see which pipes are for the coil, but there are no bleed valves on them and all connections are soldered not compression fittings. What can I do to bleed it?
EverF
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Postby rosebery » Tue Feb 03, 2009 8:07 pm

Do you have a pump? Where is it sited in the system?

Does the cylinder have a stat?

Do you have a three port valve?
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Postby EverF » Tue Feb 03, 2009 8:21 pm

Hi,

The pump is bolted to the boiler in the kitchen directly below the tank.

No stat on the cylinder only on the boiler

No 3 port valve either, the water is heated all the time the radiators are.


Of the 2 pipes that go into the cylinder (coil pipes) one is V hot, the other is just warm
EverF
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Postby rosebery » Tue Feb 03, 2009 8:32 pm

Is the pump working?

Sorry more questions:

How does the system get topped up? Is there an F&E tank in your loft? Does it have water in it?

Cheers
rosebery
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Postby EverF » Tue Feb 03, 2009 8:38 pm

Yes the pump works fine, all the rads are hot.

There are 2 tanks in the loft, one for the cylinder and one for the heating, both are full and no blockages
EverF
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Postby EverF » Tue Feb 03, 2009 8:47 pm

OK, at the moment it seems to be fixed as the water is now warm but I will have to wait a while to for it to heat up......


Basically I couldn't find a bleed valve or compression fitting anywhere so a combination of opening one of the radiator bleed valves and banging the pipes leading to the coil on the tank seems to have worked, when banging the pipes there was a kind of gurgling sound which I assume was some or all of the air passing through the pipes.


Thanks for the replies!!
EverF
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Joined: Tue Feb 03, 2009 10:40 am


Postby rosebery » Tue Feb 03, 2009 10:28 pm

I was going to suggest cycling the pump speed from slow to fast a few times. Sometimes that shifts it but it sounds as though you may have cracked it.

Cheers
rosebery
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Postby Dave From Leeds » Wed Feb 04, 2009 12:49 am

Hi EverF
I have a system very similar to yours. If the hot water is OK from now on, all well and good but if the coil should airlock again, have another look around the pipes to and from the coil. On my system the vent pipe to the smaller cold water tank (the CH top up or Feed & Expansion tank) comes off the higher of the two pipes to the coil and the water feed from this same tank goes into the lower pipe from the coil. If yours is like this, you could try fixing a hosepipe over the open end of the vent pipe with the other end attached to a cold water tap. Then get an assistant to slowly open the tap whilst you look into the F&E tank. if any bubbles come up through the bottom of the tank, leave the tap running until they stop. This should then have cleared the airlock. Be careful not to open the tap too much otherwise water may flow into the small tank too fast for its overflow to cope.
Dave From Leeds
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Postby EverF » Wed Feb 04, 2009 11:25 am

Thanks for the help guys, i'll have another look at the system tongiht and see if it is the same as yours, that sounds like a better way than banging with a hammer!
EverF
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Joined: Tue Feb 03, 2009 10:40 am


Postby htg engineer » Wed Feb 04, 2009 3:39 pm

The pump would have nothiong to do with it - if the heating is working the airlock will be in the primaries, also there wont be a cylinder stat or a 3 port valve as you say it's gravity HW.

Quick way - RGI required, remove boiler stat and boil air from the system, takes 5 mins and always works.


htg
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Postby Steve the gas » Thu Feb 05, 2009 5:46 am

I'm not as brave as you Htg.
With cast HEX perhaps, I have done this.
But the others can't take it for long.
Have you ever heard of one splitting?
Steve the gas
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Postby htg engineer » Thu Feb 05, 2009 12:48 pm

Have heard they can but I don't know anyone it's happened to - and it's never happened to me.

The reason I advise you need an RGI - even though they're not working on the gas part of the boiler - is that they should know the limits and signs it's starting to go wrong, running the boiler until it goes off at max setting on stat then removing the stat, sometimes less than a minute sometimes 2 or 3 minutes and you'll normally hear it clear with no problems and no damage.

Whereas a DIYer may pull the stat for 10-15-20 mins or more - where they're very likely to damage the boiler, it'll start venting over and possibly overflow the tank.

Although with older boilers it's always in the back of your mind - sit well back finger on spur switch, I also always make sure there's no-one in bed directly under the tank etc - don't want any injuries if the heat-ex does go ;-)

htg
htg engineer
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