Possible airlock

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We have a sink, washing machine and shower in a ground floor utility room. Cold water is supplied from a loft tank. This otherwise only feeds a hot water cistern upstairs and all other cold taps in the house are mains fed. Cold water to all the items in the utility room has stopped running after we did some work elsewhere in the house. Thinking it must be an airlock we have fed mains water through the shower cold outlet via a garden tap and hose. We opened the sink tap until the water was flowing, then turned that tap off and left the mains on until the loft tank overflowed. Alas, there is still no cold water coming through. We would be grateful for any advice please.

 

[ShaunCorbs]

Gate valve open / snapped closed ?

 

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Gate valve open / snapped closed ?

Thank you Shaun. Where would we have a gate valve? Should have said we have tried the mains flush through twice and each time the tank overflowed. So presumably the pipe is not closed off.