British Gas boiler, potential wrong expansion vessel capacity?

[bigglesuk]

I have a British Gas 330+ boiler (re-badged Glow-worm I believe) which is configured as a sealed system, installed in a four bed detached house we purchased a couple of years ago. We've had various issues with it (nothing too major) which has led me to getting quite a bit of information on it, which has made me concerned as to whether or not it's been installed correctly.

My main worry is around the size of the Expansion Vessel. The boiler has had the "integral sealed system kit" installed which from the information contained in the manual (see below) suggests is only rated to 18kW. The boiler is configured for 30kW, though can be changed via the control panel.

Am I right in saying that, if the pressure was too high in the system, the PRV would kick in to relieve the pressure? But would mean a drop in the level of water in the system leading to less pressure when not hot?

Section 5.14 of the install and service manual mentions around the sizing of the vessel. Allowing 10L per radiator (seems something a lot of websites say), with 15 radiators (and not including pipework runs) that the 150L multiplied by the 0.063 gives me 9.45L for the expansion vessel. Which is greater than the 7L vessel supplied in the kit.

I take it that this would need to either be replaced with an external expansion vessel of greater capacity? Or an additional expansion vessel added to the system, as it seems to suggest in section 5.19?

Apart from the PRV having to open, is it dangerous for the boiler to be configured to 30W with the current configuration?

Snippets from the manual: -

5.12 Sealed Water Systems
An integral sealed system kit, part no.0020051474 is available for models rated up to 18kW. The installation must comply with the appropriate requirements of the current issue of BS4814, BS5449, BS6759, BS6798 and BS7074 Part 1 and 2. See diagram 5.4 for a suggested layout.

5.14 Expansion Vessel
A diaphragm type expansion vessel, conforming to the current issue of BS4814 (see also BS7074 Part 1 and 2) must be connected at a point close to the inlet side of the circulating pump, see the diagrammatic layout, diagram 5.4. The expansion vessel volume depends on the total water system volume and the initial system design pressure. For
any system an accurate calculation of vessel size is given in the current issue of BS5449 and BS7074 Part 1. Example: For an initial design pressure of 0.7 bar, the minimum total vessel volume required is 0.063 x Total System Volume. NOTE: A higher initial design pressure requires a larger volume expansion vessel. Guidance on vessel sizing is also given in the current issue of BS5449 and BS7074 Part 1, for IE refer to the current edition of I.S.813 “Domestic Gas Installations”. The charge pressure must not be less than the static head of the system, that is, the height of the highest point of the system above the expansion vessel.


5.19 Sealed Systems
A sealed system kit is available to fit inside the case of the boiler. The kit is designed to operate up to a maximum output of 18kW. The kit contains an expansion vessel, electronic water pressure gauge and flexible pipe to be fitted in the boiler case. A pressure relief valve and auto air vent to be fitted to the system pipework.
The accessory is available as part no 0020051474, see diagram 5.6. NOTE: For systems greater than 18kW range rated an additional expansion vessel may be fitted or a proprietary kit installed matched to the size of the installed system. Ensure that the range rating of the appliance is indicated, see section 12.5 for details.

 

[Dan Robinson]

It does not matter what the rating is, it is the load.

I'd say if was undersized. But you can never have a vessel too small..

I'd be fitting an additional 12 litre vessel.

 

[dilalio]

Better to be looking at it than for it

 

[dilalio]

But you can never have a vessel too small..

Erm...

Not what she said!

 

[bigglesuk]

So my next question is going to be where to put the additional EV? The install documentation states the EV should be between the boiler and the pump, though I've seen a lot of people generally stating additional EV's should be placed close to the boiler on the return. I've attached a photo of the boiler/pipework, it seems as though coming off the pipework before the PRV would be the easiest as there is plenty of space to the right in order to put an EV.

The boiler already has a pressure sensor in it (part of the existing EV kit) so I take it I wouldn't really need to put another external pressure gauge on the system?

I was thinking of putting a 18L one in, as I'm not convinced on how good the internal EV really is and the cost difference is minimal.

 

[ianmcd]

Do you actually have an expansion problem ? check the boiler pressure at the guage when cold and put the CH on for 20 mins and go back and see what the pressure is now, a small increase is perfectly normal but if up near 3 then you do have a problem , if it isnt then you are worrying about nothing

 

[bigglesuk]

Do you actually have an expansion problem ? check the boiler pressure at the guage when cold and put the CH on for 20 mins and go back and see what the pressure is now, a small increase is perfectly normal but if up near 3 then you do have a problem , if it isnt then you are worrying about nothing

I understand what you are saying, just that the manufacturer states the expansion vessel requirements, plus I think the internal vessel is damaged internally. Would be nice to have the boiler fully functional and meeting the requirements. For the costs of put the vessel in, I think I'd rather do it.

 

[dilalio]

Just got in from a boozy Xmas plumbers party so maybe shouldn't be on here... But it helps me relax

I've read the thread again and you haven't stated what the actual problem is... If any, that has led you to all this study!
Are you experiencing issues with performance? Is boiler locking out, kettling, etc? What are the symptoms?
Have you tried properly recharging vessel?
Need more info and also sleep

 

[bigglesuk]

Just got in from a boozy Xmas plumbers party so maybe shouldn't be on here... But it helps me relax

I've read the thread again and you haven't stated what the actual problem is... If any, that has led you to all this study!
Are you experiencing issues with performance? Is boiler locking out, kettling, etc? What are the symptoms?
Have you tried properly recharging vessel?
Need more info and also sleep

The study into the boiler/CH came about originally due to general issues with the central heating. The previous owners hadn't looked after stuff at all and we had major issues with Thermostats (both room and TRVs) and also with the pressure reading on the boiler etc. Due to this I did a lot of reading up about the boiler to help try and resolve some of the issues. The system was power flushed last year to clean out all the build up that had occurred due to the poor maintenance. I believe (from memory) some water came out of the vessel from the recharge valve which suggests that the vessel has failed.

I think the largest issue we have right now is the TRV on our cylinder releasing at times, I'm trying to figure out exactly when that happens, but not sure if it is when the HW is off on the programmer. Some troubleshooting I've seen online has suggested to ensure that all expansion vessels etc are functioning correctly, but believe that should be the expansion vessel for the cylinder, not the main system. Though I'm wondering if there are some issues with the valves (given the previous issues with debris in the system) and some of the CH flow is going through to the cylinder heating the water until the TRV is required for some reason. If the HW valve isn't closing fully, then the water flowing through won't be controlled by the cylinder thermostat.

One main reason for sorting it out is to ensure that the whole central heating system is installed as it's supposed to be installed. I can T off the pipework near the PRV easily and add an expansion vessel without major hassle and not much costs, so think I'd rather just do that, better safe than sorry.

 

[Hot&Cold]

Allowing 10L per radiator (seems something a lot of websites say), with 15 radiators (and not including pipework runs)

Fellow your clutching at stray internet straws.

i can back up the above quote due to years of designing & installing sealed systems for larger properties,before the days sealed systems were common.

bigglesuk,you will need to work out an accurate water content for the radiators and add it to the distribution pipework,for 30kw to radiator circuit some pipe diameter increase is usual but that depends on how your bespoke system is installed.

Over the years of your property ownership the gas boiler & its associated parts will need maintenance by a registered gas heating technician,any mention by these technicians who will have also serviced the expansion vessel saying its incorrect

bigglesuk,please consider the rule of diversity during your radiator heating cycle re variable kw load to radiators. The manufacture of your existing expansion vessel has not been mentioned some have peak operating tolerances which are not noted on google or by .

different makes of vintage expansion vessels will have different tolerances,Your vessel may have been operating at its maximum extreme for short seasonal periods. so its time for an upgrade but get in a heating tech as its not diy

 

[dilalio]

get in a heating tech as its not diy

Agree

Jeez, I have such a hangover... Didn't deserve that, I don't think

 

[bigglesuk]

Fellow your clutching at stray internet straws.

i can back up the above quote due to years of designing & installing sealed systems for larger properties,before the days sealed systems were common.

bigglesuk,you will need to work out an accurate water content for the radiators and add it to the distribution pipework,for 30kw to radiator circuit some pipe diameter increase is usual but that depends on how your bespoke system is installed.

I agree, was just working to rough numbers, I was searching trying to get information on how to calculate the water content but there was nothing easily found apart from people stating those figures. Was just a starting point.

Over the years of your property ownership the gas boiler & its associated parts will need maintenance by a registered gas heating technician,any mention by these technicians who will have also serviced the expansion vessel saying its incorrect

Agree, I will be getting it serviced by a registered gas technician, just don't think it's had much love since install. British Gas don't have a record of installing it in our property, but I found some training manuals from British Gas in the loft (management stuff) so reckon the previous owner was a manager at British Gas and got a colleague to install it. Then, didn't maintain it at all given the condition it was in when we moved in.

bigglesuk,please consider the rule of diversity during your radiator heating cycle re variable kw load to radiators. The manufacture of your existing expansion vessel has not been mentioned some have peak operating tolerances which are not noted on google or by .

different makes of vintage expansion vessels will have different tolerances,Your vessel may have been operating at its maximum extreme for short seasonal periods. so its time for an upgrade but get in a heating tech as its not diy

The expansion vessel is one that is internal to the boiler and provided by the manufacturer, so don't know the specifications of it. As for it not being DIY, I don't fully agree. For best results yes, a heating tech is likely to give the best results, but not guaranteed

Thanks for your input (and everyone else's), it's all been very helpful.

 

[petit_pablo]

The study into the boiler/CH came about originally due to general issues with the central heating. The previous owners hadn't looked after stuff at all and we had major issues with Thermostats (both room and TRVs) and also with the pressure reading on the boiler etc. Due to this I did a lot of reading up about the boiler to help try and resolve some of the issues. The system was power flushed last year to clean out all the build up that had occurred due to the poor maintenance. I believe (from memory) some water came out of the vessel from the recharge valve which suggests that the vessel has failed.

I think the largest issue we have right now is the TRV on our cylinder releasing at times, I'm trying to figure out exactly when that happens, but not sure if it is when the HW is off on the programmer. Some troubleshooting I've seen online has suggested to ensure that all expansion vessels etc are functioning correctly, but believe that should be the expansion vessel for the cylinder, not the main system. Though I'm wondering if there are some issues with the valves (given the previous issues with debris in the system) and some of the CH flow is going through to the cylinder heating the water until the TRV is required for some reason. If the HW valve isn't closing fully, then the water flowing through won't be controlled by the cylinder thermostat.

One main reason for sorting it out is to ensure that the whole central heating system is installed as it's supposed to be installed. I can T off the pipework near the PRV easily and add an expansion vessel without major hassle and not much costs, so think I'd rather just do that, better safe than sorry.

FRom what you have described on this post the issue is with the hot water expansion and nothing to do with the size of the vessel in the boiler.
Contact a plumber who is qualified to work on unvented hot water systems as you are out of your depth.

 

[Hot&Cold]

but I found some training manuals from British Gas in the loft (management stuff)