Hot Water Cylinder Air Lock?

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19 Oct 2007
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Roxburghshire
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I've been reading all the previous posts on this forum to try to find a fix for my problem, but I could do with some pointers to ensure I apply the correct one!

Yesterday I drained the cold water tanks (two tanks are syphoned together) and removed the front one to access the other one behind it. I then fixed my original problem - a ball valve that wasn't shutting off.

I've replaced everything and added a gate valve between the two tanks. I also opened the gate valve between the front tank and the gravity fed hot water cylinder (heated by immersion heater and solid fuel fire).

During the process of spotting leaks and fixing, I accidentally left the gate valve between the two tanks closed. Leaving the dish washer on overnight (which is currently connected to a hot water feed - next job on the list; connect to cold) the nearest tank was emptied and therefore so was the hot water cylinder.

I have opened all valves and I now have hot taps that run for a short while (spluttering sometimes) and then slow to a stop.

My questions:

1) How do I know if the gate valve between the front tank and the hot water cylinder is opened properly (I have tried opening and closing a few times and it *feels* like it's working)? It doesn't look very old, but I have read on here that this could be a problem.

2) How likely is it that a gate valve has failed? There doesn't seem to be a lot that could go wrong.

3) If I have an air lock, should I try one of these methods:
a) Connect the hot and cold washing machine feeds together and force cold water into the cylinder? (Leaving a hot tap on)
b) Switch the immersion heater ON (there's no thermostat) and boil the cylinder to remove air through the pressure pipe in the roof.

Any other ideas or suggestions?

Thanks,
James

Update: Every few seconds a bubble of air can be seen in the cold water tank from the pipe that feeds the hot water cylinder.
 
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you need to use mains pressure cold to blow back the airlock in the hot
either the washing machine hoses or hose of garden tap up the hot tap spout.
 
I've given this a try (about four 20 seconds bursts) with the bath tap ON. The bath tap still slows afterwards. After turning the bath tap off there's a lot of gurgling in the hot water cylinder. There doesn't seem to be any bubbles in the cold water tank when doing this. Should I try it with the bath tap off to force some pressure further up the system (into the cold water tank)?
 
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Sounds like there could be a partial blockage in the cold feed to the hW cylinder if taps run each time for a few seconds then tail off.

Are you sure a piece of insulation or other debris didn't fall in the pipe?

Check the cold outlet in the tank is not blocked as well.
 
Thanks again 'hi-spec plumbing heating'(!) that seems to have done the trick (my wife is now happily showered without a hitch). I blasted the hot supply with no taps ON for about 2 minutes watching as the cold water tank filled up - proving that the gate valve is OK and that there are no blockages.

Thanks Dave for your reply and your suggestions. The method I used may have freed any blockages, perhaps...
 

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