If not I suspect air is being pulled down the vent pipe when some taps are in use and it is rising up to the tee afterwards.
You may be able to prove it by holding a glass of water over the mouth of the vent pipe and getting someone to operate the various taps in different combinations, see if the water disappears up the pipe.
the bigger tank has been in the same place for 30 years so confused as to why this would need raising now, it is higher than the pipework but i would say not by much, a few inches, would the AAV not relieve the air ?
So am I,I never said it would need raising. I said your cold feed may be restricted.
I suggest you go back and read the whole thread, some good suggestions been missed.
the bigger tank has been in the same place for 30 years so confused as to why this would need raising now, it is higher than the pipework but i would say not by much, a few inches, would the AAV not relieve the air ?
Something on the installation has changed in the last 30 years,the original gravity system was designed to work the way it was installed and any changes/alterations could have an adverse effect.
Also the hot water take off to the kitchen and cloakroom will have some horizontal pipework in the loft,the outlets on this branch could be pulling in air from the openvent or the cylinder is producing excessive air bubbles that get trapped in the kitchen cloakroom distribution pipe.
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