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Getting rid of airlock in Hot Water Cylinder Coil
- Thread starter jbee1
- Start date
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you are making a very very simple job sound complicated , I have done it lots of times so if its a 2 man job then I left guys in peoples lofts, what do you mean the modern way, the op has told us it is gravity HW whether that was installed 50 years ago or yesterday the gravity HW is exactly that
1-man job if your hose has a valve at the outlet end, that's why I said "likely to be".
The modern way (modern for 45 years that is), as I'm sure you know is boiler - open vent - cold feed - pump. One older way was cold feed - boiler - open vent - pump. Changed because that caused seesawing in the feed and vent pipes, drawing in aerated water. But there are other ways, my house before I uprated it had gravity HW, pumped CH return. We don't know in detail what the OP has.
Read more: https://www.diynot.com/diy/threads/...hot-water-cylinder-coil.505822/#ixzz5LdHkyeUP
No nothing to do with any pump, the OP has told you that he has Gravity Hot water, Pump is completely irrelevant, the pump is only there for the CH, are you sure that you know what Gravity HW means ????
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The significance of the pump is that if you inject water anywhere it might go through the pump instead of the cylinder coil unless you do something.
Are you sure you understand the various ways of laying out a system, modern vs old among others????
There are no zone valves on this system.
I have a gate valve near the CH pump which I closed and did the following.....
1) Took stat out of boiler and tried to boil the airlock.
2) I forced a mains water hose through the vent in the F&E tank.
3) I forced a mains water hose through the feed in the F&E tank.
The above should have cleared any air out of the coil. Still no gravity circulation.
At the moment relying on immersion heater, luckily the weather is hot so don't need to keep it on too long.
I am now convinced there is a blockage on the pipework between boiler and cylinder.
I have a gate valve near the CH pump which I closed and did the following.....
1) Took stat out of boiler and tried to boil the airlock.
2) I forced a mains water hose through the vent in the F&E tank.
3) I forced a mains water hose through the feed in the F&E tank.
The above should have cleared any air out of the coil. Still no gravity circulation.
At the moment relying on immersion heater, luckily the weather is hot so don't need to keep it on too long.
I am now convinced there is a blockage on the pipework between boiler and cylinder.
Investigate with a magnet. Suspect the H of the feed and vent and change it to combined.
A "true" gravity hot water circuit should have the vent off the top of the coil and the cold feed to the bottom.The pipes should be 1" or 28mm.I assume you mean no motorised valves, as at the very least you have pump iso valves.
That sound interesting, what happened?
With hose on the cold feed, did water come out of the vent (and vice versa)? In your original post you said you did it for 30 mins. What happened? I'd expect the F/E tank to fill in that time.
As others have said, a sketch or photos of the system would help. Most likely it's connected cold feed to boiler return - boiler - open vent - pump. Depending on just where the connections are, unless you isolate the boiler the flushing water can bypass the coil via the boiler. You can see it if you make a sketch.
Finally, are you quite sure you haven't got a valve closed in the gravity circuit? I had one once that seemed to be opening, the handwheel went a few turns (if I remember right) towards open, then stopped. When symptoms showed it was still closed I gave it more welly and it opened properly.
Yes sorry what I meant there is no zone valves.
Taking the stat was suggested to boil an airlock for a few minutes - the boiler can be triggered by the CH setting and then turned off after a few minutes.
Then the boiler continued to run and the flow and return pipes got hot.
Once they cooled down again the gravity circulation stopped so same problem as original post.
Alll seemed find in F/E tank when a hose was connected to expansion vent it came out of feed and vice versa.
The F/E has a overflow pipe which obviously prevented any spillage.
Here is the diagram of the system, its the one titled
Open Vented System with Gravity Fed Hot Water
https://www.diyhowto.co.uk/projects/open-vented-heating.htm#.W1Yf9tJKhQA
My system is exactly the same as the first one.
Taking the stat was suggested to boil an airlock for a few minutes - the boiler can be triggered by the CH setting and then turned off after a few minutes.
Then the boiler continued to run and the flow and return pipes got hot.
Once they cooled down again the gravity circulation stopped so same problem as original post.
Alll seemed find in F/E tank when a hose was connected to expansion vent it came out of feed and vice versa.
The F/E has a overflow pipe which obviously prevented any spillage.
Here is the diagram of the system, its the one titled
Open Vented System with Gravity Fed Hot Water
https://www.diyhowto.co.uk/projects/open-vented-heating.htm#.W1Yf9tJKhQA
My system is exactly the same as the first one.
That shows the gravity HW flow pipe coming out of the bottom of the boiler, which is unlikely. Probably just diagrammatic, but if it is like that it might explain how you got the airlock!
With that arrangement, the flushing water can flow down the fill pipe, through the boiler and up the open vent (or vice versa) bypassing the cylinder (as I said a couple of times). An iso valve on the boiler flow or return would stop it, but presumably there isn't one.
Presumably with an old system like this, it has worked OK in the past. If so, what has happened? Has it been drained down? If so, it might not be too much trouble to drain it again and install a valve. I don't suppose you know how it was filled and any airlock eliminated, when originally started up.
Something you might try is apply a vacuum to the vent pipe, if you can get hold of a vacuum pump.
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