Boiler overheating constantly (PRV passing)

[neelpeel]

Hi,
I have a Grant combi and the PRV is passing and constantly dripping hot water. The boiler pressure is around 2.2bar, which is close to the 2.5bar PRV setting.

I firstly vented the pressure down to 1.2 bar and it rose back up in less than an hour.
I checked the expansion tank and there was water on the air side so I then replaced the expansion tank. Problem still exists.
I disconnected the fill loop completely in case that was passing. Problem still exists.

I must have vented the system about 10 times over the last couple of weeks so there is pressure coming from 'somewhere' and since the fill loop is gone then the only thing I can think of is the heat exhanger. Do these tend to fail and allow water to pass to the heating loop? Can they be replaced by a competent DIYer?

This is a Grant Vortex 26e combi. Thanks!

 

[Chuck]

Can they be replaced by a competent DIYer?

No. Needs to be a qualified person on the Gas Safe Register.

 

[John.g]

Hi,
I have a Grant combi and the PRV is passing and constantly dripping hot water. The boiler pressure is around 2.2bar, which is close to the 2.5bar PRV setting.

I firstly vented the pressure down to 1.2 bar and it rose back up in less than an hour.
I checked the expansion tank and there was water on the air side so I then replaced the expansion tank. Problem still exists.
I disconnected the fill loop completely in case that was passing. Problem still exists.

I must have vented the system about 10 times over the last couple of weeks so there is pressure coming from 'somewhere' and since the fill loop is gone then the only thing I can think of is the heat exhanger. Do these tend to fail and allow water to pass to the heating loop? Can they be replaced by a competent DIYer?

This is a Grant Vortex 26e combi. Thanks!

Is the boiler pressure 2.2 bar and the PRV is dripping??, if so, its the PRV that needs replacing as 2.2 should be low enough not to cause a 2.5 PRV to lift.
Also, did you check the EV precharge (air end) pressure before installing?.
Suggest 0.75 bar precharge pressure and filling pressure of 1.0 bar.
If you have a 12 litre EV and 100 litre system contents then the final (hot) pressure will be 1.42 bar, with precharge/fill pressures of 1.0/1.5 bar the final pressure would be 2.1 bar.
If the pressure is still rising with a cold boiler and filling line diconnected then probably Hx problem, you might see water coming from the condendate drain with boiler off.

 

[ShaunCorbs]

Oil turn the mains cold water off to the boiler does the pressure rise ?

 

[neelpeel]

Is the boiler pressure 2.2 bar and the PRV is dripping??, if so, its the PRV that needs replacing as 2.2 should be low enough not to cause a 2.5 PRV to lift.
Also, did you check the EV precharge (air end) pressure before installing?.
Suggest 0.75 bar precharge pressure and filling pressure of 1.0 bar.
If you have a 12 litre EV and 100 litre system contents then the final (hot) pressure will be 1.42 bar, with precharge/fill pressures of 1.0/1.5 bar the final pressure would be 2.1 bar.
If the pressure is still rising with a cold boiler and filling line diconnected then probably Hx problem, you might see water coming from the condendate drain with boiler off.

Yes, 2.2 bar and PRV outlet dripping. I actually did replace the PRV as well (in error I think as I suspect the last one was fine). Maybe the gauge is slightly out as both PRVs have vented at 2.2ish.
I checked the precharge and it was around 1bar (as recommended in the manual).

 

[neelpeel]

No. Needs to be a qualified person on the Gas Safe Register.

To be clear, this is oil fired. It is also situated outside of the house so I have no concerns with fiddling with it. I have fixed it a few times over the years.

 

[neelpeel]

Oil turn the mains cold water off to the boiler does the pressure rise ?

Yes, I may try that. Good shout.

 

[exedon2]

We have changed the plate to plate on a couple of these boilers to sort this problem. Do live/work in a very aggressive water area.

 

[Chuck]

To be clear, this is oil fired. It is also situated outside of the house so I have no concerns with fiddling with it. I have fixed it a few times over the years.

My mistake. I didn't read the question carefully enough to register that it was a Grant, and hence oil, boiler.

 

[neelpeel]

Thought I would update this since folks took the time to respond.
Figured there was nothing else it could be so I ordered a Zilmet Heat Exchanger unit (£90 on Ebay) to match the label on the one in the boiler.
I isolated the feed and outlet, vented down, replaced the heat exchanger and charged back up to 1.2bar and de-isolated. All in about 40 minutes work. Then took about another 1/2hr to try and bleed out some of the air I managed to trap in the system. Remaining air managed to work its way out the little bleed-off ports and within a day it was settled and working as it should. A few weeks on now and no issues.