Water Pressure Query

[diy mad]

The PRV is a Honeywell.
Sorry to be thick but what does PHE stand for?

 

[diy mad]

This is the PRV

 

[diy mad]

Ah, primary heater exchange?

 

[Johntheo5]

It's the secondary heat exchanger in which the heat from the primary heat exchanger is transferred to the cold mains, this is a plate heat exchanger, PHE.

 

[Johntheo5]

This is the PRV

What is the exact model number, D...., can't see it clearly.

 

[diy mad]

It’s a D04 FM from Screwfix

 

[Johntheo5]

Don't know if the D04FM is drop tight or not but I think the D05 series are.

 

[diy mad]

What does drop-tight mean exactly?
What I can’t understand is that the pressure increase happens immediately the hot is switched off, I don’t think the problem can be related to hot water expansion.
Also, just noticed that the increase in pressure is different for the upstairs and downstairs taps!!

 

[Johntheo5]

Drop tight means that the regulated pressure, in your case 3.5bar, will stay at 3.5bar even if no demand for hot or cold water (static pressure control), non drop tight allows the pressure to build up with no demand but redu ess it to 3.5bar with any water demand (dynamic control).
It may just be water hammer on the hot so maybe just increase the EV size and precharge to 3.0bar?

 

[diy mad]

Thanks for all your advice Johntheo
Just one final thing, the ev is placed on the COLD water supply to the boiler, that’s correct isn’t it?

 

[Johntheo5]

Not really but goes a long way in explaining why the regulated pressure only changes when you open a hot tap, that's if you are saying that the PRV is only regulating the cold supply to the boiler ONLY? The cold will be running at pressures right up to 6 bar depending on the cold demand not condusive to good mixing, PRVshould control the total cold water supply pressure.

Edit. Sorry, misread that, yes, the EV should be after the PRV, and reasonably close to the boiler.

 

[diy mad]

It’s the EV, not the PRV that is on the cold supply near the boiler Johntheo.
The PRV is on the cold water main as it enters the house.

 

[diy mad]

Many thanks for all your help