sudden pressure drop on boiler

[marcd11]

hi im new to this so thought i’d come on and ask if anyone came across same problem..

done a boiler 2 years ago (vaillant system boiler) and its been fine whole time, lately his pressure been dropping, tops it up and lasts 4 or 5 days then drops from 1.7bar ish to 0.0bar. not a gradual drop so its strange. just all of a sudden drops fast. when this happens there is no sign of water at pressure relief. the other strange thing is when you top it back up it jumps almost straight away from 0.0 back to 1.7bar. all downstairs is wet underfloor and upstairs all radiators, no signs of leak anywhere. i have tried pumping expansion vessel up and put leak sealer in incase but no joy yet, still doing same thing. can anyone help???

 

[cjg]

have you taken it off and checked it or just tryed represured it.

 

[John.g]

" i have tried pumping expansion vessel up" Have you done it this way?.
Isolate boiler, depressurize, check E.vessel precharge (air end) pressure at 1.0bar, if 0bar pump to 1.0 bar, or, if reading > 1.0 bar, reduce to 1.0bar, deisolate boiler and open fill valves until 1.5 bar., shut fill valves.

 

[marcd11]

have you taken it off and checked it or just tryed represured it.

i have taken vessel out of boiler and checked it yes, i even had vaillant out to check boiler over and they also found nothing. engineer suggested maybe adding extra expansion, but its more cost without knowing if this solves the problem

have you taken it off and checked it or just tryed represured it.

 

[marcd11]

" i have tried pumping expansion vessel up" Have you done it this way?.
Isolate boiler, depressurize, check E.vessel precharge (air end) pressure at 1.0bar, if 0bar pump to 1.0 bar, or, if reading > 1.0 bar, reduce to 1.0bar, deisolate boiler and open fill valves until 1.5 bar., shut fill valves.

yea i turned boiler off, de-pressurized, took it out, checked pre charge, was just below 1.5 so pumped it up to that, put it back in and set it away. holds solid for 4/5 days then just all of a sudden drops to 0, then when system is re pressurized it takes literally nothing at all and jumps right back up to where pressure was at before

 

[Scott_D]

What model Vaillant?
Have you isolated the boiler from the system to confirm it’s the boiler?

 

[John.g]

yea i turned boiler off, de-pressurized, took it out, checked pre charge, was just below 1.5 so pumped it up to that, put it back in and set it away. holds solid for 4/5 days then just all of a sudden drops to 0, then when system is re pressurized it takes literally nothing at all and jumps right back up to where pressure was at before

You don't have precharge and filling pressure the same, precharge to 1.0 bar and fill to 1.5 bar, this gives a few litres of water reserve to make up for any micro bubbles collapsing and any very slight leakages.
It could also be a stuck diaphragm in the EV or (unlikely since it was removed) a blockage between system and EV.
Suggest next time you look at it and after depressurisation, release all the air pressure, then crack open water side valve, you should hear more air releasing as the diaphragm is pushed to the air end. If OK, depressurise water side again and precharge to 1bar & fill to 1.5 bar. Any doubts, renew the EV.