Unvented problem

[chilli985]

My mate has economy 7 heating and the hot water is done off
An unvented cylinder. Luke warm water kept coming from tundish
So I replaced the expansion vessel but still same problem I then
Changed the unit after the cold water mains but problem is still there
Any ideas?[/code]

 

[stardanny]

I know what causing it, but you need a G3 licensed plumber to do work on.

Daniel.

 

[ALCPlumbing]

The temperature and pressure relief may be letting by.
As mentioned you will need to someone qualified to work on unvented hot water systems to take a look.

 

[chilli985]

Daniel sorry forgot to say I am a qualified unvented installer
Just crap on faults

 

[Terry lambert]

The pressure vessel probably just needed re charging and the PRV seating may need cleaning ( a bit of carp may be in there). Or replace

I hope your mates not paying for all the parts

 

[stardanny]

The first you would check is where is the water coming from via tundish, there are two sources you need to check: pressure relief valve or temperature relief valve.

Daniel.

 

[ALCPlumbing]

In that case if you've replaced vessel the only reasons you would see water at tundish is overheating or the t&p relief is letting by. As you say water is only lukewarm I'd assume the latter. Shut off mains supply to cylinder, open lowest hot tap and drain down past t&p relief. Remove t&p relief and clean or replace. Refill cylinder and it should stop.

 

[ALCPlumbing]

You did say you've replaced the valve and prv on the inlet?

 

[chilli985]

Yeah I've replaced that unit

 

[ALCPlumbing]

I hope your friends loaded as you've already spent at least £200 of his money that he didn't need to spend.
Clean or replace the t&p relief on the cylinder.

 

[picasso]

You could have mains water at full pressure back filling the cylinder, it happens when showers ect arent balanced, a nrv gets stuck and the water at a higher pressure finds its way back to the cylinder and causes the p and t valve to open.

 

[Terry lambert]

You did say you've replaced the valve and prv on the inlet?

What cylinder, control bloc is it? Some have a separate PRV to the main control, like Heatrae Sadia.

Did yours have a new PRV as part of the control bloc

 

[stardanny]

A photo of pipework and cylinder would be great.

You need to check which it is coming from, from PRV or TRV.
If the PRV is new and not running then it must be TRV letting by. If the TRV is faulty, replace it. TRV does not open on pressure, only temperature.

Daniel.