Cross flow issues

[Why-me]

With all taps isolators closed,and the kitchen tap only hot isolation valve open,does the kitchen tap give hot water at consistent temperature ?

Nope. Shower I can't isolate and close. I already tried this and it makes no difference if all other hot valves (and cold) are closed.

 

[terryplumb]

Does it give constant temperature hot water at kitchen tap if shower is running ? All other taps isolated( hot and cold )?

 

[Johntheo5]

Might also be no harm to measure this flowrate, should be > 2.5 to 3.0LPM.

 

[Why-me]

Can't answer that I'm afraid, if you open the other two hot taps do they also get hot?
Would still suggest consider doing at least the first part of my suggested test above.
Can you take a photo of the pipework under the boiler and post the exact vaillant model and we can then see if this test is easily carried out or not.

Just tried this. Boiler set to 65, shower head open. Measured temp at other taps flowing consistently between 61-64.

 

[Why-me]

Does it give constant temperature hot water at kitchen tap if shower is running ? All other taps isolated( hot and cold )?

Yes if shower head is open then the hot water temp at other taps is 61-64. This is with all isolation valves open everywhere.

 

[terryplumb]

Your shower valve is goosed. It's the cause of the cross flow.

 

[Why-me]

Your shower valve is goosed. It's the cause of the cross flow.

Do you know if shower valves are generic replacements or does it have to be manufacturer specific? I got it from easybathrooms. Or maybe it can be repaired?

 

[terryplumb]

You would need to identify yours and source replacement parts . There is a company that specialises in shower parts .
" Showerdoc .Com UK"

 

[Agile]

I think that a simpler test would be to close the boiler cold water inlet valve and turn on a hot tap, perhaps in kitchen and see if ANY water comes out. There should be none.

Then if water comes out, turn off each cold water ISO in turn until you get one which stops the water coming out of the hot tap.

This problem can sometimes be cured by a simple non return valve in the hot feed to the faulty mixer tap.

 

[Johntheo5]

I think the the above problem points to a shower xover which affects all the taps?, I thought all showers are supposed to have NRVs on both hot and cold.

 

[Agile]

It avoids a lot of problems to fit NRVs on feeds to showers but I think this is only a trade secret used by a few conscientious people and I do not remember reading about that in any installation instructions.

 

[Why-me]

Just to update: got a plumber in to check as I can't stand the risk of leaks etc also had another cartridge on hand as standby.

The shower mixer unit actually has nrvs already fitted in the main body, the cartridge goes in between them. The hot nrv had some debris in which stopped it closing. It seemed like it was plastic pipe burr and breezer block bits. Must've happened when the builders were dragging the pipes in to position. It was just a tiny bit that wedged itself in to the valve preventing it from closing fully. Anyway both nrvs cleaned and with a new cartridge (may as well) and everything back to normal. Can't believe all this for a couple crumbs of plastic and concrete. Also thankful that we didn't need to remove any tiles as the unit is serviceable from the front behind the plate.

 

[Agile]

That just demonstrates the importance of total cleanliness.

But one sees some very careless workers sometimes.

 

[Johntheo5]

Do thermostatic controls shut off the cold water practically drop tight if turned to full HW and assuming.the HW supply temperature had fallen to say 25/30C.