Vaillant ASHP low pressure isues - fix?

[markharro]

For the second time in about 3 weeks we have this warning showing for low water pressure. The pump was installed in the summer and basically hasnt been used until about 4 weeks ago. We then got this warning. The installer came out and opened and shut the two black valve levers in the photos and it worked again. That was about 3 weeks ago. We have used the heating since then sporadically. Now the warning has come back. Surely this cant be normal!?

 

The installer showed me how to reset the pressure but I cant remember now if I have to open and shut these valves in any particular order? Hopefully someone can advise? thanks

[Beelbeebub]

You open both and there should be a whoosh sound as water enters the system.

 

You may need to turn the slotted screw on the right hand side (by the lever) so it is inline with the pipe.

 

Wait until the pressure gets to the right level (usually about 1 bar) then shut bothaand return the screw to perpendicular to the pipe (as in the picture) . To be correct you should also undo the hose and store it away, but nobody ever does that

 

A bigger question is why are you losing pressure.

 

There are 2 possibilities.

 

1) the expansion vessel (the bug white cylinder) has failed. Every time the system warms up it over pressures and water leaks out of the pressure relief valve.

 

2) you have a leak somewhere in the system.

 

Both will need looking at. Don't just keep topping up every few weeks. At best you'll rust out any radiators connected to the system. At worst you're dumping water somewhere in your house.

[JohnMo]

As you use the system micro air bubbles come out of suspension making the water volume smaller. Go around all the bleed points in the system and bleed any air out. Then reset the system pressure.

 

Do you have any water leaks?

[ProDave]

Open BOTH the black levers, one each end of the flexi pipe.  Open is with the lever in line with the pipe, they are closed at the moment 90 degrees to the pipe.  It does not matter which you open or close first.

 

Losing pressure at the start is normal as it vents any air left in the system, if it persists, then there might be a leak somewhere.

[Beelbeebub]

2 hours ago, ProDave said:

Open BOTH the black levers, one each end of the flexi pipe.  Open is with the lever in line with the pipe, they are closed at the moment 90 degrees to the pipe.  It does not matter which you open or close first.

 

Losing pressure at the start is normal as it vents any air left in the system, if it persists, then there might be a leak somewhere.

Agree, I didn't notice it was a new system. Initial venting could be the cause but this is the 2nd pressure drop and it should be stabilising by now.

[sharpener]

13 hours ago, Beelbeebub said:

You open both and there should be a whoosh sound as water enters the system.

 

Open one valve to be in line with the pipe and just crack the other open a bit until you hear water flow. Then adjust the flow rate while watching the pressure gauge.

If you open both valves fully to begin with the "whoosh" sound will swiftly be followed by the pressure relief valve going off and possibly water over your feet or elsewhere before you can react, particularly if you have not played this game before.

[markharro]

Thanks everyone. Got it reset and will keep my fingers crossed that these are just teething troubles

[Beelbeebub]

9 hours ago, sharpener said:

 

Open one valve to be in line with the pipe and just crack the other open a bit until you hear water flow. Then adjust the flow rate while watching the pressure gauge.

If you open both valves fully to begin with the "whoosh" sound will swiftly be followed by the pressure relief valve going off and possibly water over your feet or elsewhere before you can react, particularly if you have not played this game before.

good point - i should have said "open slowly". Blind spot I guess a I do this so often it's second nature.

[Helene]

Hello, what was the reason for the low pressure in the end please?

[JamesPa]

On 15/12/2024 at 09:11, markharro said:

Thanks everyone. Got it reset and will keep my fingers crossed that these are just teething troubles

@markharro This arrangement is BTW exactly the same as any sealed heating system whether ashp, gas or oil.  So any plumber can deal with it and every householder with a sealed central heating system (most these days) needs to know about it!

Edited Saturday at 16:25 by JamesPa

[Seren161]

We have a Vaillant ASHP and we were suffering with this exact issue well over a year ago.. In the end Vaillant came out, apparently a valve ( I think 🤔) had been mis spec ed and they changed it.. and the low pressure issue stopped… I haven’t been on BH for a while so only seeing this now..