532/I high/low pressure. Fix or replace?

[Aff12002]

Hello.

We have moved into a property that has a British Gas badged 532/i installed.

We had the boiler looked at before we moved in and he said the boiler was in good condition and seemed to be well maintained.

As it’s the summer we never used the heating however the hot water worked perfectly and the pressure never moved from 1bar for 3 months.

This past week I have been testing the heating and noticed a serious pressure issue. After bleeding all the radiators I pressured the system back up to 1bar and with the heating running the pressure went all the way up to 3.5. I checked the PRV to see minimal water coming out and when the system was switched off it fell to near 0. This cycle repeats if I add water to the system.

With the system at 0 I can run the heating and when operating it will go from 0 all the way up to near 2 bar. When operating in this way minimal water leaks out of the PRV and all radiators heat up.

I’ve had someone look and as expected he diagnosed the expansion vessel. He has re pressured the vessel but this doesn’t seem to have fixed as it’s still doing the exact same thing.

Is it worth replacing the vessell or at this point in the boilers life is it more cost effective to replace?

We have the budget to replace but would like to avoid if it’s not totally necessary.

Any input or further diagnoses welcome.

 

[oldbuffer]

You have 3 options:
1. Have the pressure vessel in the existing boiler replaced. Assumes the engineer opened the system while re-pressurising.
2. Install an additional expansion vessel exterior to the boiler.
3. Replace the boiler.
Hard to say without seeing it but I would try option 2 first if the boiler otherwise looks OK. See if there is a data plate on / inside the boiler (don't remove the casing) which tells you the year of manufacture.

 

[DP]

With the system at 0 I can run the heating and when operating it will go from 0 all the way up to near 2 bar. When operating in this way minimal water leaks out of the PRV and all radiators heat up.

Stop messing with the system, you are liable to introduce a malfunction due to low pressure.

I would get the expansion vessel charged up, flue gases analysed and adjusted accordingly if required, manifold pressure checked and syphon cleaned if dirty

 

[Madrab]

On a boiler that age, you may find that the PRV might have to be replaced too, as it may not seal back down properly now it's opened, needs to be checked once the EV is sorted out. Can be a real PIA to change the PRV on those boilers, due to it's location.

 

[Aff12002]

Stop messing with the system, you are liable to introduce a malfunction due to low pressure.

I would get the expansion vessel charged up, flue gases analysed and adjusted accordingly if required, manifold pressure checked and syphon cleaned if dirty

Thanks for the advice. The engineer that attended did charge up the vessell. Sorry if that wasn’t clear. It doesn’t seem to have helped in terms pressure.

So it seems either the vessel needs replaceing or the capacity is not great enough.

 

[Aff12002]

On a boiler that age, you may find that the PRV might have to be replaced too, as it may not seal back down properly now it's opened, needs to be checked once the EV is sorted out. Can be a real PIA to change the PRV on those boilers, due to it's location.

Thanks. I have defo noted that it does seem to be leaking through the pipe even when not at 3bar so that might be the cause.

That was my main concern in that the more the bill mounts up isn’t worth just swapping the whole thing to give peace of mind for the future.

 

[Madrab]

Is it the older RD 532i or the newer BG 532? Which of the front panels does it have?
BG RD 532i BG 532

Even then TBH, they were the better build of WB's IMO and unless there's a significant outlet for a large item then no real need to throw it in the bin yet IMO. Yes it's getting on now and it may be prudent to start putting a cache away to replace it but if it's still in good condition then until a major component goes then no real reason to replace.

 

[Aff12002]

Is it the older RD 532i or the newer BG 532? Which of the front panels does it have?
BG RD 532iView attachment 355910View attachment 355911 BG 532

Even then TBH, they were the better build of WB's IMO and unless there's a significant outlet for a large item then no real need to throw it in the bin yet IMO. Yes it's getting on now and it may be prudent to start putting a cache away to replace it but if it's still in good condition then until a major component goes then no real reason to replace.

It’s the newer BG532.

In the house I have 8 double radiator and 4 single. Should the stock expansion vessel be able to cope with that or shall I also look at an external as well as replacing the expansion vessel and PRV?

Thanks for all your help.

 

[Madrab]

It’s the newer BG532.

OK - so it's a rebadged CDI, nothing wrong with them, again, they're one of the better WB's albeit with lots of plastic in them where, IMO, there shouldn't be.

As far as the EV us concerned then yes, that should be able to deal with the rad capacity you have as long as the system isn't sprawling over a large footprint/area.

I’ve had someone look and as expected he diagnosed the expansion vessel. He has re pressured the vessel but this doesn’t seem to have fixed as it’s still doing the exact same thing.

If he's half the engineer he should be, he should be able to test whether the EV is shot (internal membrane burst and the valve constantly leaks water) and that a re-charge is a waste of time or whether just a re-charge (valve don't leak water constantly) done properly, there is a process that needs to be followed, would be all it needs. If he's re-charged it and it's still doing the same then he hasn't fixed the problem and should be coming back to sort it out, if he's been paid.

 

[DP]

Thanks for the advice. The engineer that attended did charge up the vessell. Sorry if that wasn’t clear. It doesn’t seem to have helped in terms pressure.

So it seems either the vessel needs replaceing or the capacity is not great enough.

The water that is in your system is locked in it- water will not compress when heated.
The expansion vessel comprises two half with a rubber membrane being the filling and crimp around the edges seals the two halves. One half is connected to the system water and other has compressed air in it.

When water is heated, expansion pushes the membrane against compressed air (0.7 bar when there is 0 pressure water side)

One has to understand operational principles of the component.

When pressurising the expansion vessel, water side has to be open so that the pressure water side is at 0 at all times and air side is pumped up to 0.7 bar. The pressure water side will still be at 0
If the membrane is ruptured, 0.7 bar pressure will not hold.
If the Schrader valve is passing, 0.7 bar pressure will not hold (change valve stem of fit extension to secure)
Such a simple task often screwed up

 

[Aff12002]

thanks for your help everyone. Even though the engineer did not drain anything from the system the pressure was reading close to 0 however I don’t think he fully drained.

I will get into this ASAP.



I understand the correct process would have been to drain to 0 leaving water open. Recharge the vessel to 0.7. Seal and then re-pressure system.

In regards to the size of the system and expansion vessell needed. My house is spread over 3 floors so as I understand there will be more pipe work than usual. I can’t say how much exactly. However I will get the original expansion checked out properly first and then potential external if it isn’t enough.

 

[Madrab]

I understand the correct process would have been to drain to 0 leaving water open. Recharge the vessel to 0.7. Seal and then re-pressure system.

Yes, if the EV pre-charge has been lost then the EV fills with water as system pressure is raised. When the system heats, the water expands, as there's (edit) no air in the EV to absorb that expansion, the water pressure keeps rising hitting the PRV's set level, the PRV lifts to release that pressure.

The system needs to be cold and the pressure released by say a drain on the boiler, that is then left open so when the EV has pressure added the membrane inflates and the pressure and the excess water in the EV is pushed out and released until such time as the system and EV reach equilibrium ~ 0 bar and no more water is released, then the EV will be pressurise to it's pre-charge level.

As far as sizing the EV is concerned, there are formulas used and the water content needs to be known but a rule of thumb is, once the EV is pre-charged, if there is more than a 0.5bar swing from the system being cold to hot, then a larger EV may be needed.

 

[Aff12002]

Yes, if the EV pre-charge has been lost then the EV fills with water as system pressure is raised. When the system heats, the water expands, as there's air in the EV to absorb that expansion, the water pressure keeps rising hitting the PRV's set level, the PRV lifts to release that pressure.

The system needs to be cold and the pressure released by say a drain on the boiler, that is then left open so when the EV has pressure added the membrane inflates and the pressure and the excess water in the EV is pushed out and released until such time as the system and EV reach equilibrium ~ 0 bar and now more water is released, then the EV will be pressurise to it's pre-charge level.

As far as sizing the EV is concerned, there are formulas used and the water content needs to be known but a rule of thumb is, once the EV is pre-charged, if there is more than a 0.5bar swing from the system being cold to hot, then a larger EV may be needed.

That’s fantastic information. Thanks very much.

Is the correct charge value for the EV 0.7 bar as has been noted here on a drained boiler?

 

[Madrab]

That’s fantastic information. Thanks very much.

Is the correct charge value for the EV 0.7 bar as has been noted here on a drained boiler?

0.7 bar is a commonly referenced pre-charge setting for a average sized system's EV.

The MI is always the place to check first though - 0.75 bar