I got called to the job and previous plumber had connected the pump to the vent pipe. Couldn't believe it actually dragged any hot water through. Tiny tank on loft as well. So Iv installed new pump, new 50gl cold water tank.
Turns out it wasn't an airlock. The gate valve was wrecked. Installed a lever valve it and seems fine now.
I did pump cold water back through the hot pipe until it came out the vent pipe in the loft. It still did not solve the problem. That's when I decided to renew gate valve. Fingers crossed that's solved it.
Yep agree it needs to be 450mm from the top. Shocking instal.
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