Hot water from cold tap!

I guess you have a Carver Cascade? If that's so, my suggestion would be that the non-return valve on the inlet has failed open, and so the pressure in the Cascade is forcing hot water out through the inlet and into the cold water pipework.

On a Carver Cascade it should be built into the lower water spigot. Should be easy enough to change, unless it has corroded in place. Probably worth changing the upper spigot too while you are there, as they seem to go brittle. They weren't massively expensive last time I did a set, but they have probably gone up a bit in price since then!

IIRC (I might not be) you can check for movement of the NRV by gently using a small screwdriver in the lower drain hole to push the valve open against the spring?

Roopert wrote:IIRC (I might not be) you can check for movement of the NRV by gently using a small screwdriver in the lower drain hole to push the valve open against the spring?

Sorry, I think I may be remembering that wrong. I think you would have to push from the other side (i.e. inside the spigot) to be able to push open the valve. Pushing from the outside will (I think) press it back against its seat, so don't push too hard!