GRANT 26 COMBI OIL FIRED BOILER. INCONSISTENT HOT WATER

[PAULRB]

Hi,
Firstly, I am neither plumber nor heating engineer, just a willing diy, have a go guy.
I have a Grant 26 oil fired combi boiler which started continually leaking water from the prv to the outside. The pressure was at 1 bar until the heating system cut in, when it would increase to 2.5 and then blow the prv.
I depressurised the system, checked the EV standing charge was correct at 1 bar [as per manual] also that it held the pressure in the tank and at the valve.... a.o.k.!
I decided to replace the plate heat exchanger, thinking this was the only cause of the constant build up of water pressure in the ch system [i.e. maybe an internal leak/split between hw & ch etc.]
Presto! no more prv leaks or excessive pressure build up, so far!
However! When installed, new [3 years ago] the water temp. on both dhw and chw systems worked fine, until this year [well before the prv leaking issue started] when running the bath, [which we do every day] the hw starts off hot then reduces to just warm, after a short while, basically not holding a constant temp. after running for a while!
Is it advisable to fit a mains water regulator, in case it's above the recommended 8 bar max.? Is there a boiler problem? Is it a service issue? Can the actuator have anything to do with it? Any answers or advice would be greatly appreciated.
p.s. The central heating is working fine.
Thanks for any help guys

 

[exedon2]

First if your boiler was installed/ commissioned by a Grant registered engineer and has been serviced its still under warranty (5 years)
Water pressure needs checking before fitting a prv.
Burner cut in as soon as tap opened?
Continue to run when tap turned off?

 

[John.g]

Simple things first, 26 kw will give you a flow rate of ~ 11.6 LPM at 40C and/or 10 LPM at 45C, so, just in case the mains pressure has increased dramatically, measure the flowrate/temp while filling the bath to rule this out.

OF boilers have primary stored water so this will give a higher flow rate for a short period but the continuous flow rate ( I think) should be then constant as above once this is exhausted, there is also a store on/off switch on the boiler, when this on the boiler will maintain this stored water at its stored temp of ~ 75C. These boilers may also have TMV to maintain the exit temp at 60C so check this out in case faulty.
The Grant combi I saw also had a DHW pump (2 pumps internally) which circulated the water through the DHW Hx (no diverting valve) but I think they just use one circ pump now with a diverter valve. Maybe thermistor fault somewhere. As above, check boiler fires up and remains fired up while drawing off water. Faulty flow switch??.

 

[exedon2]

Morning John
Grants still have 2 pumps DHW pump is on right at bottom.
Thermistor faults are known but rare if they are playing up it's normally board.
As there are a number of possibilities maybe a competent oil engineer?
Unless OP is in a very hard water area in which case some frm of water treatment needed or healing system not very clean I suspect there was not much up with plate to plate

 

[Robert Tyrrell]

Hi,
Firstly, I am neither plumber nor heating engineer, just a willing diy, have a go guy.
I have a Grant 26 oil fired combi boiler which started continually leaking water from the prv to the outside. The pressure was at 1 bar until the heating system cut in, when it would increase to 2.5 and then blow the prv.
I depressurised the system, checked the EV standing charge was correct at 1 bar [as per manual] also that it held the pressure in the tank and at the valve.*** a.o.k.!
I decided to replace the plate heat exchanger, thinking this was the only cause of the constant build up of water pressure in the ch system [i.e. maybe an internal leak/split between hw & ch etc.]
Presto! no more prv leaks or excessive pressure build up, so far!
However! When installed, new [3 years ago] the water temp. on both dhw and chw systems worked fine, until this year [well before the prv leaking issue started] when running the bath, [which we do every day] the hw starts off hot then reduces to just warm, after a short while, basically not holding a constant temp. after running for a while!
Is it advisable to fit a mains water regulator, in case it's above the recommended 8 bar max.? Is there a boiler problem? Is it a service issue? Can the actuator have anything to do with it? Any answers or advice would be greatly appreciated.
p.s. The central heating is working fine.
Thanks for any help guys

Not sure if you've got to the bottom of this but before you fit a pressure regulator just get a pressure gauge on the garden tap and that should tell you if you need one.
As for the reduction in water temperature, I would think that it's a faulty fow switch.
Good luck with this.