GRANT oil combi boiler PRV leaking

[Paul Raymond]

I had a GRANT oil combi boiler 26 fitted three years ago as a replacement for a 10 year old, failing equivalent.
Up until recently [approx. 2 weeks ago now] it has performed faultlessly. Now, since the guarantee has expired, the boiler has decided to 'kick off.'
I checked the obvious first then called my installer/service engineer, who advised me to keep a check on the issue until my service is due, as he couldn't pinpoint the actual reason for the following fault:-
The PRV is constantly running or dripping water from the overflow pipe and the temp. is showing 2.3 bar. when the CH. is running. The expansion vessel is showing the normal 1 bar static pre charge. I have also noticed an intermittent loss in HW temp. when running a bath, although the CH. temp. seems pretty constant.
My engineer suggests there maybe a cross leakage between the HW and CH supply within the system. Either the plate heat exchanger or from another source within the house, such as a power shower connected to the supply.
I have already purchased an exp. vessel and intend to buy a heat exchanger in order to save on material costs or keep as spares if not required.
Sorry, this is a bit long winded but wanted to give as much info. as possible up front.
Any ideas please? >

 

[oilhead]

Sounds like an expansion vessel failure which is easy enough to check that is causing your leaking PRV. The Grant ones discharge at 2.5 bar, so that fits with your report. I would suggest you add one of these to your spares list, as they often do not reseal after prolonged discharge. Overpressure could also be caused by a failed DHW heat exchanger, but if your static pressure stays constant,then I doubt if that is the fault.
Your engineer could also be right about the fluctuating HW temp, but I think he means cross feed between the cold supply and an outlet that does not have a non return valve

 

[Paul Raymond]

Hi,
Thanks for your reply. Just to clarify, the boiler gauge pressure SLOWLY builds up again to 2.3bar. [after I discharge via the prv] when only HW is on, but QUICKER once the c. heating is running. The exp.vessel was checked by engineer and he said the pre set pressure of 1.0 bar was correct. The HW temp. when running the bath drops to just warm, and the prv is constantly leaking water.
He was confused as to where the water pressure is repeatedly building up from, for it to reach enough pressure to blow the PRV.
As mentioned, I already have a spare exp.vessel. I can understand a cross internal leak between HW/CHW within the exchanger could cause the constant build up of pressure, but how would a build up of water within the vessel occur?
Which do you think might be the more probable cause, the vessel or the exchanger?
p.s. I will take your advice and replace the PRV anyway.

 

[ianmcd]

I will take your advice and replace the PRV anyway.

And stop using it to release the pressure

 

[Terrywookfit]

Have you disconnected the filling loop to check its not passing ?

The PHE and filling loop are the only places where the heating water and domestic water can leak.

The exp vessel and hose need to be checked properly.

 

[Paul Raymond]

Thanks for all your suggestions.
The filling loop is disconnected, so no possibility there. I'm going to order a PHE, I can assume then, that the lack of water temp. and possible internal water leak could be a coincidental double fault on the existing PHE?
I'm ok at repairing most things, anything I need to be aware of when I exchange it?

 

[Terrywookfit]

My first check would be E/V hose for blockage and E/V for charge.
Why not Test the PHE by draining and then slackening the primary connections the full mains pressure on the secondary will show if there is a leak. It will probably only be an occasional drip. Or Remove and do a Hydrostatic pressure test.

Make sure you have some new fibre washers. Also vent store properly on completion.

 

[Paul Raymond]

THANKS for your replies. I decided to replace the plate heat exchanger [even though it was just 3 years old] as I felt this was the source of the continuous water pressure build up and the consequential prv leak.
I've waited until now to test the result, and it's been successful! The pressure stays around 1 bar, and no prv overflow leaks anymore.
The boiler THEN sprung a leak which I found to be from the automatic air vent on the res. tank. I've closed the leaking bleed valve cap fully [on advice from my h. engineer] and ordered a replacement
HOWEVER, [as before this issue arose], I am STILL experiencing a drop in DHW temp. when running a bath. i.e. It's hot to start with but then fades to warm after a while.
I have noticed that when the CH is turned off it seems to run on for some considerable time before closing down. Also, if ONLY HW is run with the CH OFF, the CH flow pipe in the boiler also heats up.
Can this be a mixing valve fault [sticking etc.] and would this then affect the HW temp. issue?
I'm annoyed that after ONLY 3 years of having my previous Worcester/Bosch boiler replaced for this Grant 26E [on advice from my h.engineer] that it is having so many issues, so soon!
I intend to replace the mixer valve myself, if it's required. Do I need to be aware of anything [apart from guarantee issues, which obviously no longer count]?
Thanks again.

 

[oilhead]

Have you checked the non return valve in the DHW pump circuit. If this is stuck, it will give you the symptoms you have.

 

[Paul Raymond]

No, I havn't checked this. Any idea where it's situated in the Grant combi 26E and how to free it?
Or will it be best to replace this before the mixer valve.

Just been and checked for an nrv in the boiler pipework and found none, have to assume they are inside the pump connections ???

 

[oilhead]

Yes, it is incorporated in the DHW pump isolation valve. Isolate the pump valves, remove the pump and you have access to the non return valve.

 

[Nihad]

THANKS for your replies. I decided to replace the plate heat exchanger [even though it was just 3 years old] as I felt this was the source of the continuous water pressure build up and the consequential prv leak.
I've waited until now to test the result, and it's been successful! The pressure stays around 1 bar, and no prv overflow leaks anymore.
The boiler THEN sprung a leak which I found to be from the automatic air vent on the res. tank. I've closed the leaking bleed valve cap fully [on advice from my h. engineer] and ordered a replacement
HOWEVER, [as before this issue arose], I am STILL experiencing a drop in DHW temp. when running a bath. i.e. It's hot to start with but then fades to warm after a while.
I have noticed that when the CH is turned off it seems to run on for some considerable time before closing down. Also, if ONLY HW is run with the CH OFF, the CH flow pipe in the boiler also heats up.
Can this be a mixing valve fault [sticking etc.] and would this then affect the HW temp. issue?
I'm annoyed that after ONLY 3 years of having my previous Worcester/Bosch boiler replaced for this Grant 26E [on advice from my h.engineer] that it is having so many issues, so soon!
I intend to replace the mixer valve myself, if it's required. Do I need to be aware of anything [apart from guarantee issues, which obviously no longer count]?
Thanks again.

I have the exact same problem
I have ordered expansion vessel and PRV to replace.

Should l replace the PHE as well?

 

[Nihad]

I have also noticed that there is a small amount of drips here circled in red when l try to up the system pressure.

 

[Exedon]

That's a drain off try tightening it up.

 

[Nihad]

I have the exact symptoms on my boiler

I have changed the EV and PRV as well as the Flexi hose but still leaking PRV

How did you manage to fix yours?