PRV and TMV help please

[Dave2010]

Plumbing gods,

Today I replaced a faulty PRV with a one from screwfix it is this one

http://www.screwfix.com/p/prv-with-gauge-15-x-22mm/41943

went on a doddle however the pressure gauge is not reading?

There is a TMV fitted after it and I noticed that after you draw off some water, the TMV outlet becomes cold very quickly as though the mains cold is pushing through (does this make sense) This did not happen with the older PRV
The cold is mains and the hot is gravity from a hot water tank. I have tried reducing pressure as much as possible but this still happens. And it also appears to stall at the taps. You turn them on and some comes out then it stalls to a drip then normal service resumes, quite annoying really

any advice please?

 

[Dave2010]

guys,

looking round the net I have thought about something and would like a genius to let me know.

The TMV is directly under the water heater so practically no head
the heater outlet has 90degree bend then about 4 inches of 22mm then straight into TMV. This is then met with the mains cold.
Could this be the problem where by there is not enough hot pressure to compensate the cold which is why the TMV outlet gets cold quick??
Could this also cause the stalling problem as the TMV might intially think there is no hot flow and shut down??
The TMV has a working min of 0.2bar
This setup has been the case for 10 years for this heater on site. Other heaters use to be fed by cold storage tanks but are now mains but are not suffering the same problems

thanks

 

[Charnwood]

The TMV is directly under the water heater so practically no head

It doesn't matter where the TMV is in relation to the heater, it's the height of the tank filling the heater that determines the head of pressure.

 

[Dave2010]

[/quote]It doesn't matter where the TMV is in relation to the heater, it's the height of the tank filling the heater that determines the head of pressure.[/quote]

ah right..the unit has the cold feed tank build into the top of it.

 

[plumbplumb]

10m head height would give you about 1bar.
1m head height would only register about 0.1bar which on a gauge would probably not be visible

 

[Charnwood]

the unit has the cold feed tank build into the top of it.

So about 0.000001 bar. I can pi55 better than that.

 

[Dave2010]

So about 0.000001 bar. I can pi55 better than that. [/quote]

if the pipework were adjusted so the tmv was near the sink this would give approx 2 meters, would this provide a better head so to speak as already mentioned the cold is built into the heater so surely this cant be adjusted?