Vaillant combi boiler

My Vaillant Ecomax 824/2e combi boiler keeps loosing pressure then keeps getting high pressure, I am either topping up or releasing air with the pressure valve, however after watching a couple of Watchdog rip-off horror stories, I am a bit wary of calling in an outside firm and being charged hundreds pounds for a trivial problem which I may be able to fix with advice from the good people here on this NG.
I've read up as much as I can and by all accounts other than a leaky system it most likely appears to be a faulty and Expansion Vessel, which may either require replacing or simply topping up with air, I've checked out the cost of an OM replacement unit, which seems to vary from around 52 to 130.
I have the instruction and maintenance books which came with the boiler, the expansion vessel appears to be relatively easy to check and the pressure reading should read between 0.75 and 0.9 Bar. I haven't got a Bar meter, but do possess a reasonably good quality tire pressure gauge, which according to a conversion website says that 1Bar is equal 14.5038 PSI.
In the instructions on replacing the vessel it says to 'drain the boiler as previously described', however I've searched the index and servicing instructions in the Manual from cover to cover but can't seem to find any mention of it, hopefully this doesn't mean that the whole radiator system has to be drained simply to undo and redo a single connector? also will the new vessel have to be pressurised with air after it has been fitted?
Here's a link to the brief instructions on the expansion vessel replacement, TIA for any help in advance.
<http://dl.dropbox.com/u/11815200/boiler%20 (828%20x%201607).jpg>
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Just to preempt anyone pointing out the errors of my ways, too late I realised that 'losing' contains an extra O.
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Well, you could do that if you want to do a proppa job at vaillant's price for an expansion vessel
or ...
You could buy a pressure vessel from e.g. screwfix which will be much cheaper and install it anywhere in the primary circuit
http://www.screwfix.com/p/expansion-vessel-18ltr/26891?cm_mmc=GoogleBase - _-Datafeed-_-Heating%20and%20Plumbing-_-Expansion%20Vessel%2018Ltr
either way, yes, you will have to drain down the system unless you can ice it up.
http://www.ukcopperboard.co.uk/literature/pdfs/Installation-Tips/Pipe-fre ezing.pdf
Don't forget to put some inhibitor in when you refill the system
--
geoff

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Thanks for the advice about the cheaper alternative, however I'm wondering if it's worth paying the extra 30 for an original part, simply because it's only a matter of undoing two screws and disconnecting and a reconnecting a single union.
The boiler is in the loft well above the radiator or a hot water system, so surely I don't have to drain the whole system off simply to disconnect and a reconnect a single pipe?
<http://www.ebay.co.uk/itm/Vaillant-Ecotec-Plus-Expansion-Vessel-181051-brand-new-ORIGINAL-/280979186036?pt=UK_Home_Garden_Hearing_Cooling_Air&hash=item416baa2174

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If it's only 30 difference - go for the original. They are quite often rather more expensive

You only need to drain below the expansion vessel and a bit for comfort.
It might, however be an idea to flush it, run an anti sludge preparation through it for a day or so and then fill with the correct amount of inhibitor before the cold weather comes along
--
geoff

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On 11/11/2012 21:42, Rick wrote:

Which pressure valve are you releasing air from?

Replacing, augmenting, or topping up. Its sometimes easier or cheaper to leave the existing one alone and add another generic expansion vessel elsewhere (although at least on the Vaillant the thing is normally at the side of the boiler meaning you don't need to pull the whole thing to bits to get at it).

Yup, that is all you need. (most tyre ones will have a scale in bar as well as PSI)
Job one, is unscrew the cap on the valve and give the pin a poke. If air or nothing comes out then there is a far chance its still good. If water squirts out, then it suggests its rubber bladder has had it.
If there is no water, then you can try repressurising it. Drain enough water from the boiler so that the pressure gauge on the filling loop reads near enough zero. Pump it up to say 0.75 bar.

It normally means turn off the power, and turn off the flow and return valves at the bottom of the boiler. Quite often one or both of these also have drain points built in. If you can't see an obvious point, then slackening the union nut where the flow or return joins the boiler will let you drain the water out.
(on mine the return valve has an extra tap and a small spigot on the valve you connect a 1/4" rubber hose to for draining).
Since the flow and return valves are closed, its only the water left in the boiler itself you need to drain.

It may even come precharged to 3 bar, so you may need to let some air (or possibly nitrogen) out. If not it can be inflated with a foot pump first.
--
Cheers,

John.

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Thank's for the advice John. - Re: "Which pressure valve are you releasing air from?" - It's a big red spring loaded knob which turns about 1/4 turn and is next to the two little taps which I open to set the needle in the meter to one bar, part of this fault is that as well as losing all pressure, the reading will sometimes go way up past the green on its own, I then have to reduce the pressure using the aforementioned knob. First thing I'll do is to check the pressure in the expansion vessel and see if that's up to spec, I've checked the radiators and there doesn't appear to be any leaks or air in the system, if the EV checks out OK is there anything else he can possibly be?
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On 11/11/2012 23:36, Rick wrote:

That sounds like the over pressure release valve that will vent water (not air) out of the discharge pipe (that usually goes through he wall to outside)

Not obviously. The classic symptom of lack of expansion space is that you set normal pressure when cold. As the system heats the pressure shoots up. This will normally cause the overpressure valve to vent at around 3.5bar, and that loses some water. It then works fine until the system shuts off and cools. At which point it is usually under pressure an won't fire again until topped up.
--
Cheers,

John.

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On 11/11/2012 23:36, Rick wrote:

You need to de-pressurise the system first.
I suggest you do the following...
Turn off the boiler and open the front. Undo the cap on the valve on the expansion vessel. Press the little pin on the valve to see if you get any air or water coming out - if you get water, then it is knackered, if you just get air or nothing, then de pressurise the system, so the little needle on the boiler is showing zero It is best not to use the red knob you mentioned earlier, as this is the overpressure valve, and they can end up weeping if they get any dirt in them (the water in the system will not be 100% clean) best to use a drain cock.
Check the pressure using your tyre gauge, if it is showing nothing, or close to, then pump it up - but as the vessel is connected to the system, and will need to discharge water from the wet side, you will need to either just leave the drain cock open, or you will need to pump it up a bit, then release more water from the system until it stabilises at about 1 bar (14.5PSI) If you just leave it at 1 bar for 10 minutes or so, then re check it, to make sure it is staying there.
Once this is done, you can close your drain cock, re-pressurise the system, and bleed any air out - on my Valiant there is a air bleed on the boiler (on the pump), which if you have the same, will be ideal as the boiler is at the highest point in your installation.
--
Toby...
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Thanks, according to the book that red knob is the 'air pressure release valve', however there doesn't appear to be any mention regarding the whereabouts of the 'drain cock', which I would presume to be some kind of open ended tap underneath, although on examination I can't see anything that looks like it would fit the bill.
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<snip>
Is it just me thinking that if the air pressure release valve is being used, then after a couple of uses the air side of the expansion vessel will be empty? Which would then give the problems described.
Cheers
Dave R
--
No plan survives contact with the enemy.
[Not even bunny]
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On 12/11/2012 13:41, David WE Roberts wrote:

Perhaps a photo of the thing that Rick is twiddling might be handy?
--
Cheers,

John.

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I haven't taken a photo, however I've copied a couple of diagrams from the manual, the one I've coloured red is the thing I've 'twiddled' :-) and the two circled levers are the ones which I have to turn towards one another until the pressure reaches 1 Bar and then release, feel free to ask if you require any more information TIA.
<
http://dl.dropbox.com/u/11815200/boiler2_0001.jpg
<
http://dl.dropbox.com/u/11815200/boiler2_0002.jpg

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On 12/11/2012 16:33, Rick wrote:

I can't find any mention of "air pressure" in the manual (assuming we are looking at the same book!). Also I can't imagine a use for an air pressure relief valve in a boiler.
(there will be an air pressure switch possibly, and an expansion vessel charging valve)

That shows the over pressure release valve. Its only intended to operate in the situation where the system pressure gets too high (>3bar). (the knob allows its testing during commissioning). When it does operate it will discharge water out of the relief pipe, which it normally taken through an outside wall and terminates at an elbow pointing at the wall somewhere it is unlikely to splash anyone.
At what pressure have you been operating the valve? (it should open by itself at 3 bar)
Normally during normal operation, you would expect the sustem pressure to be around 0.8 to 1.2 bar when cold, and then to rise to approaching or just over 2 bar when hot. (the pressure rise being higher for systems with lots of primary water, and for those running at high flow temperatures)
(the blue tabs are the controls for the filling loop)

The first job seems to be to check that expansion vessel.
--
Cheers,

John.

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I don't know whether you saw my last reply to Jethro_uk, "since last evening the hot water and radiator systems have both been working OK, with the needle now staying just inside the green, which I presume is safe to operate?" If it is then all just keep an eye on it for now and see what happens, if the problem reoccurs then I will have to take the cover off and get more involved.
I've now taken some pictures of the boiler, pic 1 is where the Bar reading has appeared to have stabilised since yesterday, pic 2 is of the underside and pic 3 is of circled taps and 'pressure relief valve'.
http://dl.dropbox.com/u/11815200/boil1.jpg
http://dl.dropbox.com/u/11815200/boil2.jpg
http://dl.dropbox.com/u/11815200/boil3.jpg
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On 12/11/2012 18:14, Rick wrote:

I did, and replied there also ...

Its "safe" to operate even if it goes into the red - in the sense of that is what that valve is there to do, relive the pressure should it go to high - so nothing is likely to go pop.

Looking at those valves on the feed and return pipes, do they not also have a drain points? The picture is a bit fizzy of that bit, but it looks like it has two sets of bits you could turn. One to operate the valve, and one perhaps is to drain on the boiler side of the valve?
--
Cheers,

John.

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I have to confess John I know little or nothing about combi boilers, so this is a whole new ball game for me, however before retirement I worked in the domestic electronics industry and wouldn't dream of involving myself in anything which is liable to be dangerous (e.g. tampering with the gas side of the unit) and although I'm knocking on a bit I'm still willing to learn from people such as yourself and others on this thread who have been kind enough to offer advice.
Unfortunately the service manual I have is pretty succinct in the way of explanation, which is fair enough as it's obviously aimed as a guide for professionals and not as a detailed instruction manual for a novice such as myself, if push does come to shove then my next step will be to start dismantling and check out the expansion vessel and if needs be order and fit a replacement.
The only problem that I can see will be the draining and re-commissioning, but as I mentioned previously, the unit is situated well above the hot water and radiator system, which leaves me wondering if it will make it an easier task to replace the EV, that is as long as you good people on here don't mind me asking you seemingly stupid questions if I get stuck :-)

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On Sun, 11 Nov 2012 21:42:12 +0000, Rick wrote:

Sounds very similar to what happened to my Vaillant last year after 9 years from installation.
To replace the expansion vessel, will require the whole boiler to be removed from the wall - it is not a trivial job. However, as others have said, you can get ancillary ones, which can be added to the circuit.
However, before you do that, it might be worth checking the existing vessel:
1) remove the main cover 2) you will need to reach over the top of the boiler, and round to the back - you can't see, have to rely on touch. 3) You should be able to feel a circular fixture - like a drum head. 4) feel around the edge, and you should encounter a valve. It's a car tyre valve, with a dust cap. Mine was on the left hand side - I have no idea if this is the case for all. 5) Remove dust cap, attach bicycle pump 6) pump.
refitting is the reverse of removal.
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Sounds like a completely different model to mine, as changing the vessel appears to be a relatively simple job, according to the manual at least, did you see the link that I posted concerning the replacement procedure, if so is it the same internals as your Vaillant?
<http://dl.dropbox.com/u/11815200/boiler%20 (828%20x%201607).jpg>

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On Mon, 12 Nov 2012 13:48:50 +0000, Rick wrote:

I only saw the picture after I'd posted :(. Your boiler looks quite different.
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