Hot water from cold tap!

During our last road trip in our 99 Duetto when running the cold tap afetr a few secongs a slug of very hot water came through, seemed to happen when the pressure pump cut out although could just be a coincidence.
Anyone else experienced this and is there a cure?
Graham

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.

Thanks Roopert I suspected something along those lines, where is this valve located and how easy is it to fix?
Graham

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?

Thanks, I'll have a look at that, I'll give it a flush through as well as we have had some black bits in the water lately, maybe some of it is wedging the valve off its seat.
Graham

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!

That's OK Roopert I'd already figured that out, I drained the heater down and then switched on the pump for a short time to flush out any debris, I'm sure a ball of something fluffy in nature was flushed out so hopefully that was the problem, will see how it is on our next trip.
Graham

Good news the debris ejected from the heater drain must have been the problem as it's been fine since then.
Graham