Leak from cold water PRV when hot water turned on on boiler

[SandStone]

Hi,

When I turn on the hot water function of my gas combi boiler (Glowworm Ultracom2 35Store), I get a leak from the 6 Bar PRV attached to the cold water pipes beneath the boiler. I've had this situation for several months now, and it eventually appeared to progress to also leaking when the hot water was off (could the PRV have been damaged from the contant opening?). However, I replaced the PRV approximately two or three weeks ago, and since then it again only leaks when the hot water is on.

The PRV is downstream from a pressure reducing valve that should limit the pressure to 3.5 Bar, and upstream of a TMV, the boiler's input for heating water and the CH refill line. There's a pressure gauge on the boiler refill line, but unfortunately it's been broken for years.

Does anyone know what the cause of the leak might be?

 

[Stuckinarut]

Could be expansion related, but needs to be checked by a gas safe registered engineer and not messed with by a diyer.

 

[Madrab]

As suggested. may be time for an experienced engineer to take a look.

Little confused though - Going by the OP, this valve is a 6bar pressure relief valve?? There should be only 2 for that boiler, one for the CH (PRV - 3bar internal) and one for the HW (TPRV- 10bar@90deg on top of the boiler)

 

[Stuckinarut]

Little confused though - Going by the OP, this valve is a 6bar pressure relief valve?? There should be only 2 for that boiler, one for the CH (PRV - 3bar internal) and one for the HW (TPRV- 10bar@90deg on top of the boiler)

Yes, this threw me too. I thought initially maybe there was confusion between the boiler and an unvented cylinder.

 

[SandStone]

Thanks for the responses so far. Here's a photo of the external multibloc I have that includes the 6 Bar PRV (Altecnic–Caleffi 22mm 3.5/6 Bar Multibloc Inlet Control Valve). To clarify, all the components I mentioned are external to the boiler (sorry if I wasn't clear enough). There's an external expansion vessel as well.

 

[Madrab]

Those combi valves would usually be used for unvented cylinders.

This is getting more confusing though. The Ultracom 2 35 store - G.C. No. 47-019-15- has an internal EV for the store, so there should be no need for an external vessel. The boiler also has an internal check valve on the cold feed prior to the HW pump and HEX , so a combination valve wouldn't be protecting anything as far as expansion is concerned never mind the internal store. There is also no reference at all from Glow Worm that boiler requires a combination valve, only a pressure reducing valve, if the mains pressure is high.

 

[Rad1o]

We had a similar problem.
We kept loosing hot water from the pressure release valve from our hot water cylinder.
We have several thermostatic mixer valves. One had allowed pressure from the cold limb, which was not pressure reduced, backwards into the hot water cylinder through the outlet of the hot water cylinder. I only picked this up because we were loosing the hot water onto the roof. We have stop cocks for the cold water feed into the bathrooms and kitchens. When I turned off the stop cocks I could identify the mixer that was allowing the backward feed.
I changed the mixer valve which was a little scaled up and also fitted a PRV into the cold feed to match the PRV on the hot water cylinder.