Airlock/Combi Boiler ?

I have a closed system with a Vailliant combi boiler and am in a converted flat at the top of the building. For a few months now I've had the problem whenever I turn on the hot tap (both kitchen and bathroom) there is a delay and then a clunk and then the water comes out. In addition, whenever the cistern fills up there is a clunk in the pipes as soon as its just filled up. I had a plumber suggest to take a look at the water pressure rate but its ok (1.5 bar) and each flat has its own water stopcock so I would have thought the other flats shouldn't impact on my system... Any suggestions gratefully recieved!!

If you are in a block of flats it could well be that your water comes from a communal storage on top of the roof outside. If this is the case you should have it converted to the real mains. 1.5 bar is exceptionally low for mains so this is most likely the problem of your noise appearing when you open the dhw. I have never heard of an airlock in a mains.

You could try cleaning the nylon hot water inlet filter. It is possible that the Hot Water Heat exchanger is cruddy (It may be the original type and not the sardine tin ) A number of things to check out

Just wondered if you had solved the airlock problem below as I have exactly the same problem with a vaillant boiler. Started recently after we had a new shower room fitted.

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I have a closed system with a Vailliant combi boiler and am in a converted flat at the top of the building. For a few months now I've had the problem whenever I turn on the hot tap (both kitchen and bathroom) there is a delay and then a clunk and then the water comes out.