Tap mystery

[Paul Andrews]

This isn't really a problem, but it does intrigue me.

Our bathroom sink has a single mixer tap. it's one of those fancy (italian) ones with a tilting lever control - left to right = hot to cold, down to up = off to on.

It's working fine, but it does intrigue me.

If it's set more to cold than hot, then turning it on (lift lever) then turn left (towards hot) usually results in the water flow becoming colder before it gets hotter. I'd be inclined to think it's because hot and cold may be in proximity in the pipe work, but that would make me understand why the cold was hotter to start perhaps, but not getting colder when initially turned to hot.

Perhaps it's haunted? ;-)

Paul

BTW the water (H&C) is under pressure from a pump.

[Mike Halmarack]

Access the nearest compression joint and pump a few litres of Holy Water through the contraption, that'll fix it.

[Paul Andrews]

LOL, never thought of that... ;-)

[Guy King]

The message from Mike Halmarack contains these words:

Get a Pope on a Rope?

[Mike Halmarack]

It's a faith thing. :-)

[Mike Halmarack]

Aren't you thinking of Mussolini?

[Guy King]

The message from Mike Halmarack contains these words:

I get on very well with the street lighting people round here!

[Mike Halmarack]

Always best I think, in case they single out your specific house.

[Aidan]

Twin impeller pump, cold is under more pressure (don't know why) and so flows up the hot pipe. Turning to hot discharges the cold water before the hot water arrives.

Maybe a dodgy pump, the hot side impeller has been partially shredded by cavitation?

[Paul Andrews]

Maybe, I suppose.

Well, the pump is about eight months old...

[Aidan]

It was a flying guess, but no other suggestions have been offered as yet. It shouldn't happen with 2 identical pumps turning at the same speed. A reduction in the flow rate of one pump would usually cause higher delivery pressure, so one pump couldn't push water against the other. It suggests to me that the performance of the hot side pump has deteriorated compared to that of the cold.

Cavitation (i.e., hot water boils in low pressure inlet; vapour bubbles then implode on entering HP outlet) is a common fault on the hot side, because of the high temperature. Excessive restrictions in the hot pump inlet makes it more likely. It will take bits out of the impeller, which are usually plastic & only rated to 65 degC anyway. See the instruction manual for more info. Cold feed to hot water much further up the cold water tank? Hot pump drawing in air from the top of the HWS storage cylinder (no Surrey, Warix, etc., flange on hot outlet) ?