unvented cylinder discharging

[fogarty]

Been to relatives house to check a water leak showing through ceiling. Leak coming from tundish on OSO indirect unvented cylinder. Unfortunatly this didnt happen while I was there but they think its hot water discharging not cold. The last time it happened was when the shower was run. I tried shower and hot taps but no discharge. Apparently a different plumber told them it was the t&prv,charged £250 but still does it. When t&prv is turned hot water discharges through tundish some of it spraying out of gap down side of tundish and pipe onto ceiling. Blown down drain after tundish and its clear.Cant see anything wrong. If it was thermostats they would cut out before hot water discharged through tundish and need resetting but they seem ok. Any help appreciated

 

[Mbear]

Discharge the pressure in cylinder( turn off mains and open hot taps). Recharge the hot water expansion vessel(usually White in colour) to whatever the badge says with footpump. Reinstate mains and close taps when water starts to come through. I can pretty much guarantee this vessel will be either flat or burst. If it's burst obviously replace it mate

 

[oldplumber]

might be sensible to investigate discharge pipe diameter as it sounds as if the discharge pipework is to small, hence overflow from tundish. Also wise to call in a plumber with unvented ticket to do work on this system to comply with the regs. note, replacement expn vssl/prv should be supplied by unvented manufacturer.

 

[migoplumber]

agree with mbear, but you probably shouldnt do it, call in a pro to be sure.

 

[fogarty]

Thanks for replies. I do have my unvented ticket but I'm only a trainee plumber and real life is much trickier than college. The expansion vessel read 0.8 bar so pumped it up to the 1 bar required. The discharge is 22mm after tundish, 15mm before but pipework dissapears into hidden internal drains so cant size discharge exactly. If expansion vessel was shot wouldn't it read zero?