Grant Vortex Pro - Pressure Relief Valve dripping

4 Jan 2010
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United Kingdom

I've got a Grant Vortex Pro combi installed in 2017.

I've just noticed that the out let pipe from the PRV is dripping. I've had a plastic bag over it to see how much it is dripping and I would say its a couple of teaspoons over the past 5 hours.

Central heating hasn't been on since April, so only using hot water. The pressure gauge is where I normally have it...about 1.2 to 1.3 BAR.

I've read there can be an issue if these fire off and they don't re-seat properly but I'm not aware that the PRV has fired off because it reached the 2.5 BAR limit. It seems unlikely that it would only take the pressure back down to 1.2 BAR if it fired off.

So my questions are:

If the PRV goes off, does it take pressure right down to zero or would it take it back to about 1.2 BAR?

Can the PRV just start letting by, even if it hasn't fired off?

Is there anything else I should be looking at?

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As above check expansion vessel
If prv needs replacing the correct one is 2.5 bar
They can be 'interesting' to do very easy to damage brazed on socket they fit in.
If your boiler had the low pressure swith on it I would get rid of that at same time just wire it out 1/4 plug needed to blank socket.
They are not now fitted and can snap very easily!
Also check flexi to expansion vessel in dirty systems they are known to block.
Possibly, even if unlikely, the PHE?. but PRV shouldn't drip until > 2.5bar.
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To be fair it's not totally unknown for plate to plate to fail we have changed a couple on Grant combi's in last 5 years .
Should add the area I live/work in has water described as aggressively hard!
Thanks for all the replies so far guys.

So I checked the expansion vessel this morning. Seems OK. Static pressure holding at 1Bar.

PRV hasn't dripped since yesterday and I've been checking the pressure gauge regularly and it seems steady (about 1.2 bar and goes up a bit after hot water store is primed).

The wife mentioned she thought the hot water was hotter than normal this morning (scalding she said). Could this be a sign it is something to do with the plated heat exchanger?
Not sure re the Grant but some heat the water to ~ 80C and then reduce it to 60C via a TMV which may have developed a fault.
Yes there is a TMC factory set st 50c.

Big sticker on it saying do not adjust so I've never touched it
So I checked the expansion vessel this morning. Seems OK. Static pressure holding at 1Bar.
means absolutely nothing, you have to check it the correct way, there are no shortcuts, but it doesnt sound like an expansion problem , going by what you have said

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