T&P valve passing water constantly

[TedStriker71]

Hi,

Bit of background. I have a 180L Stelrad unvented cylinder, professionally installed 6 years ago into a 30 year old house which previosuly had a vented CH & HW system, and had no problems with it until now. Went away for a couple of weeks and returned yesterday. Unfortunately while away my heating was completely off and the house was around 4-5C when I got back. The pressure reading on the boiler was too low for the boiler to fire up, but that's happened a few times before and a quick top up from the fill loop sorted it out. So the heating and hot water went on and it all seemed to be working but today I've noticed that there is a constant flow of hot water from the outside pressure relief pipe. I feel this may have been happening all night as I could hear more noise than I'd expect from the house but I put it down to the heating working overtime to get the house up to a normal temperature again.

Looking at the tank, I can see a constant flow of water into a tundish. The water is hot. I have turned the mains water off and the flow has stopped but it starts again as soon as the mains water is turned back on. If I twist the red cap on the T&P valve anticlockwise, the water flow into the tundish gets much faster - so fast that it overflows into the HW tank cupboard. Once let go, it goes back to the constant flow, probably a couple of litres a minute at a wild guess.

I've attached a picture which hopefully will help but it seems to me that the T&P valve is stuck open - even though the mains water has been turned off. The tank is full of hot water but not excessively hot. Too hot to hold your hand under for more than a couple of seconds, but nowhere near scalding.

The boiler is a Vaillant ecotec 812 HE system boiler.

Please ignore the mass of cabling - it's the remnants of a decommissioned house alarm system

Any and all advice would be much appreciated!

Cheers,
Ted

 

[terryplumb]

Call in a G3 certified engineer to examine , rectify issues ( and perform a service if due. Should be serviced annually)

 

[Madrab]

If the water is hot then yep, it's more likely to be the temperature and pressure relief valve (T&PRV) that passing. It is activated under either excessive heat or pressure or if it has failed. I wouldn't think that it was just because the temp dropped to ~ 5 deg but never say never.

As it's one of the safety features of the UV cylinder then you will need to get a qualified engineer in to look at what the cause may be, rule out that the cylinder isn't overheating or over pressuring and replace the valve if needed.

 

[TedStriker71]

If the water is hot then yep, it's more likely to be the temperature and pressure relief valve (T&PRV) that passing. It is activated under either excessive heat or pressure or if it has failed. I wouldn't think that it was just because the temp dropped to ~ 5 deg but never say never.

As it's one of the safety features of the UV cylinder then you will need to get a qualified engineer in to look at what the cause may be, rule out that the cylinder isn't overheating or over pressuring and replace the valve if needed.

Thanks, would you expect this to be covered by the warranty on the tank? Pretty sure it was at least 10 years.

I mentioned the cold as it seems rather a coincidence to me that it would happen the night I get back.

Should I be concerned about the tundish not coping with the flow of water when the T&P valve is fully opened by twisting the red cap?

I would get a plumber in but with the recent and upcoming weather it will be many days before that's possible so was wondering if there's anything I could do in the meantime. I can't see an isolation valve anywhere so have to keep the mains water off until I need to use cold water in the house. Heating seems to be working fine though, which is nice.

Cheers,
Ted

 

[Madrab]

You say it's a stelrad, not familiar with them as they make radiators. Is it a Stelfow perhaps? Can you given the model number or a clear pic of that large label?

Warranty would cover it if it can be proven that it was installed correctly ( benchmark) and subsequently serviced properly (service history) every calendar year. If not then they probably wont cover it.

Bit of a failing of the installer too that there was no isolation point fitted upstream of the combination valve, school boy error IMO.

 

[kidgreen61]

Neat wiring

 

[TedStriker71]

Neat wiring

I guess you missed this bit... 'Please ignore the mass of cabling - it's the remnants of a decommissioned house alarm system'