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Message started by molegrip on Oct 11th, 2017, 5:57pm

Title: Baxi Expansion Vessel substitution
Post by molegrip on Oct 11th, 2017, 5:57pm

Ok, an old chestnut...
The pressure on my old Baxi 105e drops like a stone once it reaches full temperature.  I put a jar under the outside overflow pipe and it fills up with H2O very quickly.  Suspected knackered Expansion Vessel therefore.  The only reason i can carry on using the boiler is i fitted a rigid filling loop so its easy to re-pressurize before starting up every time.  Many reasons why this is highly undesirable, not least that the system now has no inhibitor in it at all.

Three probably dumb questions - 1) if i fit an external Expansion Vessel running off a heating reaturn pipe (which i think i can do) - does that cut out the old knackered expansion vessel automatically if its still connected inside the casing ?  If the flow keeps going into the old one then i'll obviously keep losing the water.   2) - i don't get the route by which the water from the wrong side of the expansion vessel finds it way out to the overflow pipe and into my yard ?  3) And last, looking at new substitute expansion vessels i see there are ones without and ones with a whole 'Sealed System Kit', involving a manifold with a pressure gauge, pressure relief valve, and flexible hose and one-way valves etc.  Is that the better option ?  Looks complicated.

Many thanks in pressure  ;D

Title: Re: Baxi Expansion Vessel substitution
Post by woodsmith on Oct 12th, 2017, 3:49pm

Unfortunately our plumber is currently sunning himself somewhere foreign so you can take any plumbing advice from me with a pinch of salt!

But, you say the pressure soon drops once the boiler is fired up but if the expansion vessel was faulty I would have expected the pressure to rise before the pressure release valve opened. If you are not seeing a pressure rise first as a chippy it would seem to me that it is the pressure release valve that is faulty rather than the expansion vessel.

The expansion vessel has a rubber diaphragm across the middle, if this fails it shouldn't leak water out. They are usually set to about 1.5-2bar and are designed to take up the expanding water as the temperature rises. The pressure release valve should only open when the system pressure gets above something like 3bar. So if your system is not getting up to 3bar and you have water in the outlet from the valve this is why I think it's probably the valve faulty rather than the vessel.

Title: Re: Baxi Expansion Vessel substitution
Post by molegrip on Oct 12th, 2017, 5:23pm

Thanks Woodsmith.  

Yep, overnight it occurred to me that i might be barking up the wrong tree blaming the expansion vessel for such a big loss of water.  I know how it started - it was reading in the past that low water pressure might be caused by a fault in the EV.  But i added 2 to 2 and got 5 - jumping to the idea that a drop in pressure linked to a big loss of water might be an EV problem.  But i couldn't see how water from the EV got out and down my overflow pipe into the yard - hence one of my questions.

I've always been influenced by one odd thing about my boiler which i only inherited in December - someone in the past has done a bodge by fitting a continuous filling-loop (flexible hose) between the cold main and the flow pipe to the central heating.  There is a tap on it so it can be isolated, but the tap was open when we arrived and i thought this bodge was a cheap way to fix a more expensive problem - like eg having to take the whole bolier off the wall to replace the EV !  It's on the wrong end of the manifold really - filling-loops as far as i know should be between the cold main and the Return side of the CH not the CH out-flow side ?

Ok, the pressure-relief valve - one of the reasons i wasn't considering that, was that i fitted a new one early this year, and i fitted a new air-bleed valve and a new diverter diaphragm kit - all simple jobs.  But i am thinking that as the pressure-relief valve was NOT a Baxi part but a cheap ebay clone - maybe it's faulty ?  I have fitted a new rigid filling-loop on the right side, so i can easily re-fill and put the pressure up to 0.5 bar in a few seconds every time i want to fire up the boiler - and it does run well.  The water pressure climbs nicely to the correct 1.5 - 2.0 bar when it's up to temperature - never above 2.0, but the water starts running freely out of the overflow pipe and soon fills up an old coffee jar.  Not long after the boiler is switched off, the water-pressure drops to Zero.  A couple of days ago before i fitted the filling-loop, the old girl made a very nasty noise when i tried to start it, and the 'Failed pump / Low pressure' failut-light came on and it shut down.  Presumably the pressure had hit the floor even below what the clock can show.

I'd be grateful for any opinions as to the cause of this big water-loss.

[ Just thought - it's weird that the pressure drops to zero on the clock when the 'bodge' permanently open filling-loop on the left of the system is connected to the cold main - it has a grey unti on it which i'm guessing is a pressure-reducing valve to cut the mains pressure down. ]

Thanks again.

Title: Re: Baxi Expansion Vessel substitution
Post by woodsmith on Oct 13th, 2017, 11:49am

You should pressurise the system to about 1bar when cold and it should rise to about 1.5bar when hot. The expansion vessel should be operating at this pressure which stops it fluctuating wildly. If you are getting big variations in pressure as it heats up that may show that the expansion vessel is not working.

The filling loop should have a non return valve fitted. These look like an isolator valve without the screw stop tap. A pressure reduction valve is much bigger and will often have a gauge and an adjustment knob integral to the valve.

I have a biggish central heating system with 17 radiators and that has an additional expansion vessel which works alongside the expansion vessel in the boiler so I would imagine it would be ok to fit another expansion vessel to your system if you think yours is faulty.

If you are losing water overnight it has to be going somewhere. If you can't find a leak and there is not enough water escaping from the pressure release valve then is it possible the water is going back down the filling loop?

You are right the filling loop should be connected to the return pipe on the boiler.

I have seen a boiler with the filling loop permanently left open, the boiler was mysteriously losing pressure and they couldn't find the fault so just left it running at mains pressure. Not a good idea though as, apart from anything else, the system would probably be running at a very high pressure most of the time. I was fitting a kitchen there so thankfully not my problem.

Title: Re: Baxi Expansion Vessel substitution
Post by molegrip on Oct 13th, 2017, 7:56pm

Thanks again.

I'll do it with numbers to stop me rambling ;-)  -

1)  The water doesn't disappear overnight - it shoots out the overflow pipe pretty soon after the boiler reaches top temperature.

2)  I start it at 0.5 bar, and it runs perfectly at 1.5 - 2.0 bar, never above - so if the pressure relief valve is venting it is doing it at too low a pressure.  I have ordered a new one given they are not much more than a fiver.

3) The old permanent filling loop does have all the right valves in it including a pressure reducer marked 3 bar - but when i turn it full on, the clock pressure does not rise, so its not doing its job for some reason.  Maybe it cannot work cos its on the flow side of the CH ?  This is a bit of a red herring anyway as i'm aiming to make it redundant.

4)  Today's news :  i managed to get the plate off the top of the boiler which covers the chamber at the back where the expansion vessel is housed - took a bit of demolition as the previous occupants had dry-lined over the back two screws !  This revealed that yes, the expansion vessel is kaput - i pressed the schroder valve in and H2O came p-ssing out immediately, so i'm presuming the diaphragm split aeons ago and the whole EV is full of water.

5)  So the pressing practical question is one you referred to - how about fitting a new EV near the boiler on the return side of the CH.  Now that i've found the existing EV is totally full, i'm not worried anymore abut it still playing a part in the system - Except...IS there any connection between that full EV and the constant loss of water, or is that just a faulty PRV ???  Does the fact that there is nowhere in the EV for expanding water to go force it out of the PRV into the outside world, even though the clock pressure never shows more than 2.0 bar ? (so shouldn't the prv stay shut?)  Having never worked on one before, i've no real idea about the pipework running from the expansion vessel and how it empties to the outlet pipe when it gets full up.

I will return - gotta eat!


ps:  just noticed yr "an adjustment knob integral to the [pressure reducing] valve.".  Thanks - something else to find and play with.

Title: Re: Baxi Expansion Vessel substitution
Post by woodsmith on Oct 14th, 2017, 9:16am

3/ take it all out.
4/ brilliant, there's your problem. Pressure release valves seem to be designed for limited use. They easily stick open if used so if you had just swapped the valve you would have soon had a reoccurrence of the problem as it needs a new valve and expansion vessel to be fitted at the same time.
5/ the new expansion vessel should come as a kit of parts, you will need some pipe and a T fitting but then just follow the instructions you get in the box. They come in different sizes, if you find the size of the one in the boiler you could match it or get the next size up.

Best of luck, hopefully this will solve the problem and you can put some inhibitor in the system it may need it!

Title: Re: Baxi Expansion Vessel substitution
Post by molegrip on Oct 14th, 2017, 2:26pm

Thanks Woodsmith,

My neighbour stuck his head under the boiler this morning - its tight as its just above a worktop - and found the adjusting screw in the middle of the pressure reducing valve which i'd never seen.  Its in the middle of the bodged filling-loop i mentionned.  (#3)  It was screwed down way too tight and that was why it wasn't sending any mains water to the system at all.  I tweaked it to the right and have now got rock-steady pressure at the clock at 0.75 bar or wherever i want to set it - great.  That at least means i have no problem with the boiler starting as its always got enough minimum pressure.  I'll leave that loop in place until i solve the problem of the constantly dripping leak to the outside.  New pressure relief valve should be here on Monday - first job to eliminate that possible problem.

I'm pretty confident about fitting a new expansion vessel as long as it can go under the worktop about two feet from the boiler t-'d into the return pipe from the nearest radiator.  I'm interested in what to do about the old EV - i can get to the top of it (just), and i can see the bottom fixing nut and the feed pipe to the prv manifold.  I'm not sure whether i could get it out without taking the whole boiler off the wall, which is the recommended method - i'd love to know if anyone has ever slid it out of the space at the top after undoing the bottom fixing - if one had a big enough gap between the boiler top and the ceiling...the diameter of the EV is about 16" so its quite a lump to squeeze out the top with the low ceiling i've got.  But if it could be done then a new Baxi style EV could slide back in.  But as i say the manual says no, boiler Off the wall, no debate.

Given that there is a steady drip of water to the outside pipe - presumably the PRV must be at fault whatever else is going on, as there's no other way out for that leak.  Will report back after a new PRV fitted.

Many thanks for the input - who needs the plumber  ;)

Have a great w/end.

Title: Re: Baxi Expansion Vessel substitution
Post by woodsmith on Oct 14th, 2017, 5:24pm

Ha who needs a plumber! Well you haven't fixed it yet and he will probably tell me I should stick to woodworking when he gets back :D ;D

Title: Re: Baxi Expansion Vessel substitution
Post by molegrip on Oct 14th, 2017, 8:46pm

Ahhh that's true, let me re-phrase that...

It has been thoroughly TALKED about without the plumber...not fixed!  ;D

Title: Re: Baxi Expansion Vessel substitution
Post by CWatters on Oct 22nd, 2017, 5:58pm

I see no reason why you can't leave the existing expansion vessel in place and just add a new one (same size or bigger) elsewhere.

The old one would only be a problem if it rusted through.

Replace the expansion vessel and Pressure Relief Valve (PRV) at the same time as once the PRV starts to let water through they are prone to leaking.

Title: Re: Baxi Expansion Vessel substitution
Post by molegrip on Oct 28th, 2017, 3:18pm

Many thanks - yep, i've got a new PRV ready to fit at the same time as the new expansion vessel.  I will leave the old one in place for now - i can see it from the top of the Baxi with the steel plate removed and i toyed with the idea of trying to get it out upwards after releasing the water pipe at the bottom, but all the guides/manuals say its a boiler-off the wall job so i chickened out.

I have a convenient place under the work-top for the new EV, but i'm a bit baffled by all the bits that came in the kit with it.  I don't get what the one-way vales are for as i thought the water must be able to flow freely back and forth between the radiator return pipe and the EV ?  The bits look like what one would  use for a filling-loop ?  I will attach photos of all the bits in the box if i can.  Later i will mock-up the connections i'm guessing would be needed to get yr thoughts.

One thing i really should know - does it matter which up way up the EV goes ?  And similarly, should the PRV in the kit be used (and the pressure clock), and if so is it important for the PRV red cap to be facing upwards ?

Thanks in advance !

[Having trouble uploading my gallery of pics...]  :-?  
Oh, i see - if you click on View member's gallery, there are 5 pics.

Title: Re: Baxi Expansion Vessel substitution
Post by woodsmith on Oct 29th, 2017, 10:22am

You have bought a kit so it includes a filling loop plus valves, and PRV. You don't need to fit them for the expansion vessel to work. I have seen people recommend fitting an isolating valve between the return pipe and the expansion vessel but that is bad practice. As for which way up to fit the vessel, most plumbers fit them with the connection to the top but I would expect there are instructions with the kit which will show you which way to connect it. The last one I fitted specified fitting the connection to the bottom.

If you have bought a new PRV that fits in the boiler then I would fit that otherwise you could use the PRV that came with the kit.

If you can easily see the pressure gauge on the boiler I wouldn't bother fitting the one that came with the kit.

I don't think it matters to have the PRV valve to the top.

Title: Re: Baxi Expansion Vessel substitution
Post by molegrip on Oct 30th, 2017, 10:23pm

Thanks Woodsmith.

I found an official-looking website that said the expansion vessel should always have the spigot facing down and the pipe to the heating system rising at a slight angle  upwards !  I know people have successfully fitted them all which ways, and some are even on their side.  I'm going with the neck downwards which just happens to put the text on the italian manufacturer's label the right way up.

Yes, all those bits were my fault really - i ordered the 'Sealed system kit' when all i really needed was a vessel !

Thanks for the thought about an isolating valve between the vessel and the heating pipe - i was going to fit one for obvious reasons but if its bad practice i won't.

I've got hold of a 3/4 bsp Tap connector which fits the spigot perfectly and it reduces to 15mm so i can get to the T on the return pipe with a couple of 15mm elbows and about 18" of copper pipe.

Yes, i have a working pressure gauge on the boiler already, and the new PRV ready to fit when its all drained down, so i contacted the ebay seller and they offered a refund if i returned all those un-needed bits - but i might just keep for future jobs.

Disappointed there were no instructions in the box even though it came from a leading brand.  Would have been more of a problem in pre-internet days!

One thing i'd love to know if you know a Baxi guy - is it totally impossible to get the original expansion vessel out without taking the whole boiler off the wall, or can it be wriggled out of the top space after removing one steel plate which goes across the back right against the wall ?  It looks tempting, but i'm not in an adventurous mood right now so the full EV is staying put.

Will be tackling sometime this week when the inhibitor arrives.  Looking forward to not heating fresh cold mains water from the filling-loop, only to spray it out steaming into the yard at a rate of knots !

Onwards !

Title: Re: Baxi Expansion Vessel substitution
Post by thescruff on Oct 31st, 2017, 8:58am

A very rusty looking plumber returns  ;D

Not sure I like what I'm reading lots of safety issues :o

Anyway, as you say.

The expansion vessel has lost its charge, or
The expansion vessel diaphragm is split, or.
In a new system could be undersized.

Perfectly ok to fit a remote vessel as near to the return as possible.

PRVs nearly always leak after they have been activated so renewal is best

Title: Re: Baxi Expansion Vessel substitution
Post by woodsmith on Oct 31st, 2017, 9:29am

thescruff wrote on Oct 31st, 2017, 8:58am:
A very rusty looking plumber returns  ;D

Not sure I like what I'm reading lots of safety issues :o

I knew I'd be in trouble [smiley=horse.gif]


Title: Re: Baxi Expansion Vessel substitution
Post by molegrip on Nov 5th, 2017, 7:10pm

Welcome back the real plumber !

Yep, the diaphragm was split - water fountain out of the schroder valve or whatever the right name is when i pressed the pin in.

I fitted a new PRV first - stupid little upside-down grub-screw ;-)

I fitted a new 8L expansion vessel only a foot from the return pipe just underneath the worktop above which the boiler situated.  No service valve fitted as recommended.

Most fiddly bit was getting around the way i had to pre-fit the EV holding bracket cos the angle of the screws made it impossible to do once its on the wall, but because the wall was some old dry lining had to tape the butterfly fixings to the board to stop 'em drifting about when i offered up the complete EV plus bracket.  It all went good and secure eventually.

VERY happy to say the boiler is now for the first time since we moved in last December working like a new one.  I set the cold pressure to 1 bar, and it only goes up to 1.5 when fully hot, and the EV is taking the expanded hot water as required.  Brilliant.  Big bonus that the whole system is so much hotter - rads untouchable, and there is no leakage to to the outside over-flow pipe so the new PRV working perfectly.  Thanks to all help received!

If i can ask a completely different question - if i run the hot water side a lot - such as for a bath - the rads all get warm even if i set the boiler to the Summer 'Water Only' position.  I recently replaced the diaphragm and other bits in the front diverter unit so that's fine, but is there a job to do in the bigger manifold behind the front diverter unit ?  I can see that both micro-switches are working.  Sorry about the lack of technical terms - i'll look at the maintenance manual later to get the correct terminology.

Onwards !

Title: Re: Baxi Expansion Vessel substitution
Post by thescruff on Nov 6th, 2017, 12:16am

I would have suggested a slightly larger vessel, 12Ltrs whereas 8Ltrs most be a tad small.

Diverter. valve is the normal problem.

Title: Re: Baxi Expansion Vessel substitution
Post by molegrip on Nov 6th, 2017, 6:25pm

That's interesting - i thought of using a 12L vessel early on, but ended up with the 8L only because that's the size listed in the original spec for the Baxi 105e.

Thanks for the tip about the diverter valve.


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