Ariston Classico HE STD 150 unvented cylinder leak

catwin · Feb 8, 2024

Good evening,

I'd like your opinion on something that is worrying me please: my landlady's plumber replaced the bottom/night element of my 20-year-old unvented cylinder (an Ariston Classico HE STD 150) 5 days ago and I hadn't noticed that it was leaking. He fixed the leak today but now the tundish is dripping very fast. I am reading online that it means the pressure release valve is faulty or water pressure in the system is rising too high and the tank could explode, but the plumber says there's no risk and he'll come replace the release valve tomorrow (he says he tried to stop it but it seems to be stuck slightly open). Can he be trusted? And should I get an annual inspection from an Ariston partner (Surge Renewables) from now on, at my expense? Thanks!

EDIT: I have shut the water off at the mains and switched the tank off, and opened all the hot water taps until they stopped running. Can I open the mains water again so I can at least have cold water?

Basher · Feb 8, 2024

I believe it's quite common for old pressure relief valves to leak after they have been adjusted after a long period of sitting there at normal mains pressure 'not doing anything'.
I believe your plumber is correct, and given the valve is leaking, it's not stuck shut, so I think there is very little likelihood of an 'explosion'.
Unvented cylinders are supposed to have an annual check/ service. That instruction should be in the owners manual, though not everybody does it! Having it checked periodically is a good idea, but it should be your landlady's responsibility, in fact I believe it's one of her legal obligations.
If it were me I would turn the water back on. If you are not running the immersion heater there should be no danger from increasing pressure. The immersion has both a thermostat and a separate safety cutout, so the chances of it heating the water to boiling point are incredibly remote, especially with a new one.

catwin · Feb 8, 2024

Basher said:
I believe it's quite common for old pressure relief valves to leak after they have been adjusted after a long period of sitting there at normal mains pressure 'not doing anything'.
I believe your plumber is correct, and given the valve is leaking, it's not stuck shut, so I think there is very little likelihood of an 'explosion'.
Unvented cylinders are supposed to have an annual check/ service. That instruction should be in the owners manual, though not everybody does it! Having it checked periodically is a good idea, but it should be your landlady's responsibility, in fact I believe it's one of her legal obligations.
If it were me I would turn the water back on. If you are not running the immersion heater there should be no danger from increasing pressure. The immersion has both a thermostat and a separate safety cutout, so the chances of it heating the water to boiling point are incredibly remote, especially with a new one.

Thank you, that's reassuring 🙂