Vaillant Combi Boiler - whats going on with indicated pressure?

[Fallingditch]

Vaillant 832 plus LPG combi boiler supplying 8 radiators on ground and first floor.

 

All radiators have been bled.

 

There may be a weeping leak in the ch system, but if there is I can't find it.

 

The boiler has an LPG LCD screen.

 

I come down first thing in the morning and the system is showing (maybe) 0.4 bar which means it won't fire until I pressurise the system.

 

 

So I open the mains supply valves for maybe 0.25 seconds and let a little water into the system to pressurise the system to (say) 0.9bar, at which point the boiler fires and heating is supplied to the rads.

 

As the system heats up, the indicated pressure climbs, and tends to settle around the maximum (say 3.6 bar).  (However it can rise to 4 bar + which sometimes causes the system to shut down automatically).

 

As part of my test, I then switch the time switch to OFF, and the system starts to cool down.  After (say) 30 minutes, the pressure is often showing 0.4 bar, which means I have to re-charge the system to get more heating … and then the cycle repeats. 

 

(Because the system currently is on most of the time, the pressure is usually showing 3.4 bar.  However during the overnight shutoff (or if I turn it off as a test) system temperature reverts to ambient, pressure drops to < 0.9 bar, and the system wont fire until re-pressurised.

 

Can anyone suggest what's going on here?

 

[ProDave]

Expansion vessel has failed, usually the air bladder inside has ruptured.  The pressure should not rise that high if the expansion vessel is working properly.

 

Get it replaced ASAP, not something you want to ignore.

[Fallingditch]

Thanks for that @prodave. Vaillant confirm the fault looks like an 'internal issue', and will be covered by warranty.

[ProDave]

8 minutes ago, Fallingditch said:

Thanks for that @prodave. Vaillant confirm the fault looks like an 'internal issue', and will be covered by warranty.

Good news, that probably means the expansion vessel is built in.  Do let us know what they change to fix it.

[Fallingditch]

On 08/12/2022 at 18:47, ProDave said:

Do let us know what they change to fix it.

After a nightmare few hours on Vaullant's not-fit-for-purpose telephone call queuing system, I eventually got a service engineer out under warranty.

 

The expansion vessel was OK; the problem was with some combination of malfunctioning pressure sensor, and malfunctioning pressure release valve, and auto admittance valve.  they replaced all three.

 

Essentially, the boiler was discharging small qualnities (drips) to an externally mounted pressure relief pipe throughout the day - so that caused the pressure to fall to 0.3 bar and the system to require daily recharging, but without giving that much of a clue .

 

The displayed pressures of 3.4 bar and 3.6 bar were probably exaggerated, and caused by the faulty sensor. Thx for your help @ProDave

[ProDave]

Thanks, glad you got it fixed.