Pressure Reducting Valve - adjustment

The GMan

Hi I have this pressure reducing valve on our heating system, it has both a screw and a knob, anyone know what the correct way to adjust this one is. I read that you screw out to reduce pressure and in to increase. But on this model is it that on the screw or the knob or both ??

The GMan

OK so this looks to be one of these .. more correctly an "Automatic Filling Valve"

The screw on the top A is for "regulating the downstream pressure".

An the Knob on the bottom D is "Mains water volume and flow control and isolation valve"

Still not sure how to adjust it correctly, OK Screw A out to reduce pressure and in to increase. But what to do with Knob D and when ?

John.G

With the system cold Open valve D fully (antoiclockwise), slowly screw down (clockwise) A until water stars flowing, fill the system very very slowly, gradually screwing A clockwise until filling stops at 1.5bar, tighten down the locknut on A. Advise strongly to then close D fully and only top up the system when the pressure falls to 1.0 bar cold, you can let A as is permanently.

The GMan

Hi John.G Thanks very much for the instructions.

I've done that there now and it's seem stable at 1.5bar.

I understand your logic for shutting of D, but does that not negate the "automatic filling" functionallity of the valve ?

I'll keep an eye on it, but I suspect I must have a leak somewhere as it shouldn't have dropped to zero like it was.

John.G

It does negate the "automatic filling" functionallity of the valve I'll start at the start.

If your EV has been correctly pre charged (that is the pressure at the air end with no pressure at the water end, or the air end pressure before installation of the E.vessel) to 1.0bar, then that filling pressure of 1.5bar means that there is now 2 litres of water in a 10 litre E.vessel, this is known as the reserve, so this will make up for any microscopic air bubbles collapsing etc and if/when the 2 litres is used up then the pressure will be back to 1.0bar (cold). nomally this will last 6/8 months to 18 months, if you have to top up the system say every 2 weeks or so then obviously a leak somewhere. Now of course you don't know, if in fact, your E.vessel was correctly pre charged or not, if it had been precharged to 1.5bar then obviously no water reserve with probably little no leaks despite frequent top ups.

Also gas boilers and increasingly now oil fired boilers with internal E.vessels have generally speaking smaller E.vessels and by having the pre and filling pressures the same then the smaller E.vessel is big enough to keep the (hot) system pressure to say 2.5bar as a bigger one with pre/filling pressures of 1.0/1.5bar.

Because of this and people getting fed up with frequent top ups......enter the Auto fill valve where the pressure always stays at 1.5 bar but your rads might well be rotting away due to a relatively small leak and the continuous auto replacement with oxygen rich make up water of which you will now be blissfully unaware.

One other thing, watch the pressure when the system is fully hot and note the pressure, also there will be a PRV (safety valve ) on the boiler with the waste pipe from this generally exiting a wall nearby so watch this for any dribbling, it may be leaking even though shouldn't lift until 3bar.

The GMan

Hi John.G

Thanks again for your reply and for taking the time to respond in detail.

I don't see any seperate expansion vessel so I'm assuming it's interanal to the boiler, it's a Vokrea 25s gas boiler.

I can't see the watse from the boiler PRV as it seems to routed into the nearby waste for the washing machine.

When the boiler went on for a few minutes, a quick look accros from the attic door seem to show it close to 3 bar. Now it on for an hour or so and the rads are all hot, and preressure is about 2.5 bar.

The fact that the pressure had droped to zero and that it took some messing to get he auto-fill valve to respond at all this morning (screwing in and out all the way), makes think there must be something wrong somewhere either a leak or possibly a fault with the valve ?

thanks agian

John.G

No leak, the expansion vessel has either lost its precharge pressure or the diaphragm is punctured IMO especially since the pressure went to 3bar before the system was all fully heated, you will have to get a GSR certified service person the check that out, you probably have a 8 litre E.vessel precharged to 1.0bar.

When the system cools down you should see the pressure well < 1.5bar since you have now lost some water from the E.vessel.

The GMan

Hi John

The Vokera 25s seems to have an internal expansion vessel of 8L alright, according to the documentation.

But as you say as if that's the problem we are into getting a registered installer to sort it.

I'll chaeck the pressure again later when it's cool.

thanks again