How do I cure the pressure loss in vaillant ecotec plus 831

[hardy1015]

Hi, We have a Vaillant ecotec plus 831 boiler, it worked fine for about a year, we are now getting F22 fault code, the boiler constantly loses pressure and we have to open the two valves underneath to re-pressurize the system, we are doing this now on a daily basis, we had Vaillant out who told us there is a leak somewhere in the system and no problem with the boiler, it has been happening since January, 3 months! Surely if we had a leak we would be aware of smell or mustiness somewhere in the house, we have absolutely no signs at all, the house seems to be watertight, we then got the LDS Leak Detection System people in and they could not find any leaks, they were here for two days! We are very confused as to why an expensive branded product like Vaillant should be causing us so many problems, we have had another two plumbers out one to service it and another to put some leak stop stuff into the system, neither of these made any difference whatsoever, please help if you can with a possible solution to this conundrum! Thanks..

 

[mcmoby69]

try here //www.diynot.com/forums/viewtopic.php?p=251090#251090 first.

 

[flameport]

we had Vaillant out who told us there is a leak somewhere in the system and no problem with the boiler

They are probably right.
If pressure is dropping, water is being lost somewhere.

The possible options are:
a. Leaking pipe / joint / radiator - could be anywhere including places you can't get to or see.
b. Pressure relief valve is faulty
c. Expansion vessel failed or not charged, which will cause water to leak out of the pressure relief valve when the system is heated.

If they have already examined the boiler, that should eliminate b and c.

Another possible option is a leak in a hot water cylinder coil where the cylinder is supplied from a cold water tank, however as your boiler is apparently a combi it is somewhat unlikely that you have a hot water cylinder as well.

Leak sealer is designed for tiny little leaks on old systems which would result in pressure dropping over a period of weeks. It may work in some of those situations.
There is NO way it will seal a large leak or hole, and iin your situation it is totally useless and shouldn't have even been suggested.

 

[hardy1015]

Hi, Thank you so much for such speedy response, I have made a note of what you have replied and we have yet another plumber coming out soon to hopefully carry out some tests in line with the replies that we are sent. Many Thanks..

 

[ChrisR]

One thing to try is
Turn the boiler off. Double Plus off..! Take the fuse out!
Then turn off the isolation valves under the boiler on the flow and return, for a night.
If the pressure in the boiler drops, the leak's in the boiler.
If the pressure holds up, but drops suddenly when you open a valve to the system inthe morning, then the leak's on the system.

Leaks on either can be elusive - for a little while.

 

[Whitby]

Probably the heat exchanger:
I recently had this problem. I checked every rad & bit of pipework but no leaks anywhere.
Had a local heating engineer out who replaced expansion vessel, but to no avail, still losing pressure every day.
Then got vaillant out, they fitted the legendary conversion kit, but was still losing pressure, so I got them out again & the replaced the heat exchanger which had a crack in it allowing water to escape causing the pressure to drop, since this has been replaced the boiler has worked like new, mind you it is only 6 years old! I had one vaillant engineer who never spotted it was the heat exchanger, the next engineer sussed it straight away.