Cold water coming out of hot taps

[MSaxp]

Hello,

I have this puzzling problem in my house. I will provide as much info as possible, not sure what is relevant. I dont intend to fix this myself, just want to help the plumber and have some idea of what the fault might be

The house is a 9 year old house, has an unvented cylinder (Range Tribune HE).

When you turn on a hot water tap at full, the water will eventually get warm (never super hot). Following that, if you reduce the flow to 50%, the water will turn cold again. If at the same time, you turn another hot water tap on , then both will flow hot water again. So the temperature seems to be a function of the flow.

Oddly enough, it also seems to be linked to the flow allowed by the central stopcock. The less the flow at the stopcock, the less flow you need at the taps to get hot water. So lets say the tap is at 80% and flowing cold water, if you then reduce the flow at the stopcock, the tap flow will reduce (as you'd expect) and the water will get warmer.

All of the above just refers to hot water taps only. Mixer taps are lukewarm at best.

Does the above make any sense? Sounds like there is a faulty valve somewhere that is allowing cold water in the hot system depending on the overall system pressure??

Any ideas would be very welcome.

Thanks,

Mike

 

[picasso]

Non return valves on showers are the usual suspect, followed by mixer taps, can you isolate any of the taps, showers ect and see if it cures the problem?

 

[MSaxp]

Thank you. I have already replaced 1 shower and the kitchen mixer tap, so only one shower left. I will cap that and see if it makes any difference.

If its not that, is there a chance it is caused by either the dishwasher or the washing machine?