Secondary expansion vessel needed with new boiler?

[Rich1974]

Hello,

I've searched the forum and can't find anything on this so here goes...

We moved into a new build two years ago. It's a two bedroom house with one shower and seven radiators, and a Sime Format 80C boiler. The boiler has never been great, running hot and cold, making all sorts of dodgy noises. Six months ago we had the thermister replaced and filter cleaned, this solved the temperature problems but not the noise.

(Incidentally, but it may be worth mentioning at this point, we then had one of the large double radiators replaced by two small four-column ones of these:

About a month after having these two radiators fitted the pressure began to drop on the boiler. We were then topping it up with the filling loop at least every two days.

The boiler died last week, the Corgi registered plumber said it was knackered (needed pump, expansion vessel and PRV) and that he could fit a new Glow-worm Betacom 30 condensing combi for £1000 all in. Deciding to cut our losses and get rid of the clanky, inefficent (SEDBUK D) Sime, we went for it.

After a week without heating or water (and a distressed fiancee) the boiler was fitted last night... and lasted three hours. The pressure dropped overnight and needed topping up at 6am. Then it dropped again. I turned the boiler off and topped it up again to 2 bar - it dropped to 1 bar in 40 minutes flat, while off. It then shut itself off. I reset it, which made no difference. The plumber came out and cranked it up to 2.5 bar before it would come back to life.

There are no obvious leaks. I've taken the plasterboard off around where we had those two new rads fitted and it dry as a bone. The rads are all bled, can't find any air in the system. The boiler is blowing off water into a bucket at the mo (he's coming back to plumb it into the washing machine outflow) and he advised us to leave it running at about 2.5 to 3 bar until he can come back next week. Since he left two hours ago it has been running at 2.9 bar and everything is fine, not dropped at all and all the rads are hot.

To the crux: the plumber then suggested that we have too many radiators for the system, and need a secondary expansion vessel fitted alongside the new boiler. I just need to know if this is standard practice, as it seems strange to buy a new boiler and then need an add-on. We were originally going to buy the 24k version of the Glow-worm, but got the 30k at the plumber's suggestion - believing it to be adequate for our system.

It also doesn't help that he's one of the nicest blokes you could meet, so I hate questioning him! Thanks in advance for any help.

Rich

Rang Glow-worm's Tech Help line (50p a minute!), the bloke who seemed employed to just say "Yeah" said "Yeah" when asked if fitting a secondary expansion vessel was usual practice.

Our old Sime may have been largely rubbish, but it was 24k and managed to heat all our radiators on high just fine. So why does a new 30k Glow-worm need another expansion vessel to do the same job?!

 

[CharterGAS]

if you have more than 8 rads you wil need an extra expansion vessel - you need about 1L per radiator as a quick guide

sounds like the boiler has gone onto a sludge up system and sludge has partially blocked up the pressure switch!!

did yo get a powerflush with the install and more importantly has the engineer down rated the central heating side of the boiler?? i guarantee you don't need 30kw to heat your house!

 

[Rich1974]

Thanks for the reply - it did get powerflushed but I have no idea about down-rating the central heating side... what is that, and will I sound like I'm insulting his intelligence if I ask him?!

Just to confirm then CharterGAS - you think the boiler is the right size for our house, but it does need a secondary expansion vessel?

 

[leakylea]

If you are losing pressure at the boiler with the system off, you have a leak, do you have pipework under your floors downstairs? a small leak beneath there will drop the system in minutes.
Or if the filling loop has been left on and is passing slightly it wiill build up and your prv will function taking the pressure right down again.
Its doubtful i know but i had a Halstead boiler that had a slight leak on heat exchanger and was runnig down condensate pipe.
To isolate your boiler from the system by use of valves you would see if you have a boiler problem or system problem
pressurise boiler and system to 2 bar then isolate boiler on valves
give it a while and check gauge on boiler if this is the same 2bar boiler not leaking but if you open the valves up and the gauge drops rapidly you can be sure thers a leak on your radiators and pipes somewhere
make sure that the plumber has not been draining system whilst working on it by manually operating prv this will have grit behind it and is the cause of your woes good luck

 

[plumbnuts]

The advice given is not stricktly true. The pressure in the boiler when the system is totaly cold should be just above 1 bar. At 3 bars the pressure relief valve will operate and spew water from the 15mm pipe that should be routed outside the property. If the boiler has been pressurised to 2.9 bar by the installer it will loose water/pressure as above. As for your old boiler, the expansion vessel rarely goes and usually just needs re-charging. Is your instlaller registered as he doesn't appear to know what he is doing. £1000 is far too cheap for the job to be done properly i.e powerflushed, commisioned, registered with building contol etc etc.
If you would like further advice send me a private email.
Steve

 

[Rich1974]

Thanks for all the advice. This has moved on a bit so the title is not relevant any more but I wanted to update you.

Plumber came back, re-pressurised the expansion vessel with a bike pump and it worked fine on constant for a week, rock solid at 1.8bar. Then flicked it back on to the timer and it dropped to zero in two hours.

Got Glow-worm out, boiler is fine, PRV bone dry - we have a leak *somewhere* in the pipes. Nice to have spent £1.2k on a new boiler to find this out. There is no visible trace of a leak at the rads but all our pipes are buried under solid oak and Yorkshire stone flooring and in the walls. This is not going to be fun, especially as we're going to have to get the useless feckers at the NHBC involved

 

[fatoftheland]

Szing the heating side of the boiler is not so important as the hot water side as the boiler will modulate from about 5kw to 30 kw depending on the return temp. If the boiler is dropping pressure when not in use you have a leak. If nothing is apparent inside, check outside to see if there is a drain cock or 2 letting by. Its a fairly big leak so I would not advise using leak sealer. NHBC are structural only. You may want to talk to your Insurance co.

 

[bonesy60]

There are thermal imaging company out there that can trace leaks on systems that are sealed in walls and floors may be a cheaper way in the long run as you only damage the area needed to repair the leak.

 

[smiley plumber]

erm £1000 very cheap for the job done plus PRV should not be blowing into a bucket even tempory into a bucket ! 2.5 bar far to high need to be 1 to 1.5 check the presure in the exspansion vessel need to be 0.5 bar as norm but could be rased to 1.0 bar if slightly bigger system
if still rasing to 3. bar and blowing then it may need a bigger vessel you need to work out how many litters of water in the system there is a chart available from vessel manufactures to help with these things but if your plumber knows what he is doing then he will have sorted all this

 

[payney1974]

erm £1000 very cheap for the job done plus PRV should not be blowing into a bucket even tempory into a bucket ! 2.5 bar far to high need to be 1 to 1.5 check the presure in the exspansion vessel need to be 0.5 bar as norm but could be rased to 1.0 bar if slightly bigger system
if still rasing to 3. bar and blowing then it may need a bigger vessel you need to work out how many litters of water in the system there is a chart available from vessel manufactures to help with these things but if your plumber knows what he is doing then he will have sorted all this

i think the condense was in the bucket

 

[smiley plumber]

ahh did i read it wrong then lol never mind

 

[stevetheplumber]

i think the condense was in the bucket

i hope the bucket was tested to be part of a flue system

 

[Puddle]

i hope the bucket was tested to be part of a flue system

nice