Page
last edited
Friday, 02-Jan-2009 19:23:30 GMT
Diverter
Valve Diaphragm Replacement on the
Worcester
Bosch 24CDi Combi Boiler
(Note: If the step-by-step images do not appear
down the left hand edge click
here
to load the page properly)
[EDIT:
Many thanks to all the e-mails from others who have attempted this
repair having read these pages - I usually get at least one e-mail a week from others successfully implementing this repair, thankfully most of them succeed with less drama than the one quoted at the bottom of the page! Whilst this walkthrough was never intended to be
a 'How To' guide it's good to know that it has proven to have been an
inspiration for others to give it a go. With that in mind, I cannot
stress enough how important it is for you to acknowledge that this still
isn't meant as a guide and that if you are not competent to safely
carry out the work you should get a Corgi-registered (boo.. hiss..! ;-)
) professional in instead. It is probably worth reading the e-mail at the bottom
of this page and ask yourself if you're really upto tackling the
problems you might face when doing it for the first time!]
'What's
this got to do with house renovation?' you might well ask...
Well, as every DIYer knows all too well there's many a job that gets
itself uninvited on the To Do list. These jobs are
invariably unforeseen, involve fixing something, and indeed don't do
much more than return to you to the state you were in before!
Nevertheless, they've still got to be done and can quite easily cost a
fortune if you get the pro's in. They do say 'a fool and his
money are easily parted' and I like to consider myself no
fool. Or perhaps I'm just tight-fisted. Either way, I decided to tackle
this particular job as given I'd already sussed out the problem there
was no way I was going to pay someone else to implement the fix, not
least because it would've be quite pricey given the labour and
all-too-common (yet avoidable) 'repair by replacement' attitude of some so-called professional heating 'engineers'.
Anyway,
back to the original question, I put this page up as I could find very
little information on the web covering this particular job and whilst
the boiler service manual covers the mechanics and internals of the
appliance it doesn't instil much confidence in the ability for a
'DIYer' to do anything more than use the boiler every day, and get
someone in to 'service' it every year... Despite this I thought I'd
'have a go' and in order to enable me to get the boiler back together
again I took some pictures along the way... They proved invaluable, and
hopefully they might be of some further use if anyone else decides to
give it a go... if only to put the words/drawings of the service manual
into 'real life' pictures.
The
reason
I ended up spending half my weekend with my boiler in pieces was due to
a problem with the shower suffering from temperature fluctuations. The
shower, a thermostatic Mira Excel, was only 18 months old and indeed
top-of-the-range so something was clearly amiss. Whilst the shower was
on, the boiler could be seen to 'dropping out' whereby it would fail to
recognise the demand for hot water. Furthermore, if a (hot) tap was
opened whilst the shower was on the boiler would usually run without fault. All this
pointed to some fault with either the shower not demanding enough water
to keep the boiler on, or the boiler failing to recognise this demand.
I
originally suspected the former and set to work dismantling the shower.
Having installed this myself I recalled a pair of inlet strainers which
I suspected may have been blocked thus reducing the flow of water. This
turned out to be true - the hot water inlet was partially blocked with
what I could only describe as 'black stuff'. It looked like either dirt
or plastic? Either way I was surprised, and confused, given that I'd
installed all the pipework and taken great care with flushing the
system prior to final commissioning. Still, it was in there and
shouldn't have been so I cleaned the strainers and reassembled. The
problem, however, persisted.
I
then
started to wonder what this 'black stuff' was. Investigation into how
the boiler works revealed that the diverter valve contains a rubber
diaphragm which sits inline with the hot water (DHW) supply and who's
job it is to activate a microswitch when a hot tap is opened (in addition to diverting the water through the water-to-water heat exchanger rather than the central heating curcuit). This
information alone was sufficient to make me suspect the diaphragm has
perished and thus not only was it unable to do it's job, but was also
responsible for the blocked shower inlet.
I
contacted Worcester Bosch only to be told that 'repair' was by
replacement of the entire diverter valve and, at £70+vat (and labour),
I was a little annoyed. Whilst I was not 100% sure I was pretty
confident that it was only the diaphragm at fault - the rest of the
valve (i.e. the actual diverter bit that controls
whether the heated water in the primary flows through the radiators of
water-to-water heat exchanger) appeared to be working okay.
Some
further trawling of the web revealed the diverter valve was made by
Giannoni - a supplier of valves for numerous other makes of boiler.
Fortunately some of these other makes do sell the
diaphragm without having to buy a whole valve. So, I bought one for
£15 (order code 112501, and even badged as a Worcester-Bosch
spare, from
www.keeptheheaton.com) - although I'm sure if you shopped around you find them cheaper (particularly as this was back in 2004).
The
rest
is detailed through the captions on the photos. If you're going to
tackle this job you ought to have a copy of the official Worcester
Bosch service manual as I've kept the detail brief on the assumption
that anyone reading it would also have this manual. [Edit: It
used to be easily available from the Worcester Bosch website but now
appears not to be - you can therefore download it from me here
(1.4MB PDF)]. Needless to say, if you're not totally
comfortable ripping your £800 boiler apart (I
wasn't!), then think twice about doing so... Having said this the labour
charges you'll save doing this yourself, not to mention the inevitable
knowledge gained through ripping it apart thus saving you even more
money in the future, makes it a worthwhile challenge...
Finally,
needless to say, I should point out that the diverter valve is right in
the heart of the boiler
thus numerous other (expensive) bits need ripping apart first...
Repairability of what is clearly the boiler's achiles heel
certainly didn't feature much in the design stages of this boiler!
Good
luck! :-)
As
mentioned I get many e-mails from others describing how they've managed
to replaced their boiler diaphragms, some go more smoothly than
others... (name withheld to protect the guilty!)
Hi Mathew.
Are you sitting comfortably........................... Then I'll begin.
You were quite correct, there were more local suppliers of the parts, much more helpful and the ability to get them over the counter enabled me to ask questions and get some advice.
The task was a bit of a marathon though. Stripping down went well enough, though I almost fell at the first hurdle. When I opened the drain taps, nothing happened. I ended up taking the white plastic centre parts of the tap out completely, and still no water. In the end, I stuck a small screwdriver in to the centre of the tap body, and cleared out much black crud, and hence the system drained.
Putting back together was a different story all together. The diverter valve itself went in OK, but the "bent pin" clip holding in the bypass pipe just would not go in. After a number of removals of the divertor valve to check the hole was OK, and the O-ring seated properly, I eventually decided the only way to find out what was happening was to take the bypass pipe out all together. Out of the boiler housing, the pipe fitted so easily it was scary.
Now all I had to do was get the old O-ring out of the connection at the right hand side, which I thought would take ages, but in fact came out quite easily with tweezers. So I put the diverter valve back in, put the bypass pipe back in, and still the clip would not fit. In the end, I had to lift the right hand end of the bypass pipe from it's housing to allow the left hand end to be fitted first. Now it located and the pins went in first time - the right hand end also went in easily. No-where is this tip documented, but really it cost me 2 hours of trying because I thought if I took the right hand end out I wouldn't be able to clean the joint and replace the O-ring without removing even more parts from the boiler.Obviously, I hadn't been able to clean out the seating faces of the hole in the pressure valve body, but the new O-ring seems to have sealed anyway.
The heat exchanger went in easily - it was the last easy part of the job.
The first attempt at putting the filling loop in place seemed to go OK, but pushing the unit rightwards to locate into the inlet valve was very stiff. The left hand end located up OK, and the water was turned on. The reason for the stiffness became apparent, the little O-ring on the right hand end had caught somehow, and broken, with the obvious result once water was applied.
So water was turned off and what was left in the boiler drained again. The filling loop removed, O-ring replaced, and a second attempt made. This time the right hand end seemed to locate more easily. The left hand end screwed down, and the boiler filled. A few drips from the left hand end of the filling loop were stopped by tightening the screws, and all looked good. But the pressure didn't come up, and the boiler wouldn't turn on. Double flashing reds suggested no water pressure, but water had definitely flowed into the boiler, and the hot water taps would run, but obviously not heat the water. After much head scratching, and repeated turnings of the filling key - I eventually tried turning the
little grey knob - water flowed into the boiler, and straight out of the left hand end of the filling loop mating surface!!! In the blind panic of having water all over the place, I dived underneath to turn off the valves again, and disloged the front panel from it's hinged down position. It fell floorwards, but I caught it before it pulled the pressure gauge pipe out, which was very fortunate.
Stripping the filling loop out again, I found the metal bracket hadn't located over the mating surface properly. Screwing the filling loop down had located it against the support bracket, but not fully against the actual mating surface on the diverter valve. This was corrected, the loop refitted, and water turned on again. This time, no immediate signs of serious leaks. A bit of drying up was required before I could turn on any electric, but eventually the switch was thrown.
Well, the pump would run, but still no heat. I could hear the igniter ticking, but no flames. I couldn't tell if this bacause the gas wasn't being turned on, or there was no spark at the igniters. The flashing lights indicated an electrical sensor fault, and in investigating this the broken cables were found - remember I said the front panel had fallen.......
Now - I should be able to do electronics - but all the cables listed in the manual, and visible on your photos were in place. In fact it was the igniter cables that had pulled out. So I have to get to the controller board and re-attach these cables, but where and to what I couldn't tell at this point.
I should probably point out that to get the controller board out, you have to remove the 3 control knobs. The manual does say "carefully", but they are very stiff. The hot water control knob came out easily enough, they are just a simple knob with about a 2.5 inch shaft. The central heating control was much tighter, but came eventually. The On/Off just didn't want to move. A heave with a pair of pliers brought it out though - but the shaft was only an inch long, and had an ominously jagged end. So, the on-off controll knob was broken, a length of it's shaft was still in the panel (so I couldn't use one of the water control ones) and of course, the swich was set to the off position.
I'd really had enough of the job by this stage, so I decided to put this control knob issue off until later, and deal with the problem I had started to fix, i.e the reconnection of the electrode wires. I managed to get the controller board lifted, but the location of connectors for these two wires is not listed in the manual, and there was no indication of if they were polarised. I took an educated guess, found a relay that had no wires on it's output, and pressumed that polarity would not be an issue to the electrodes of the igniter probes - and with heart in mouth took the soldering iron to the loose wires.
Now it really was anybody's guess if I'd soldered the igniter wires to the correct part of the controller board, so I could be about to send a spark to the gas with no reference to any logic. But I still couldn't try it out, because of the broken control knob. However, on close inspection, the shaft is basically round, with a flat edge to locate and key into the switch body, and there was at least a cm of shaft with the flat here - so I stuffed it in and hoped there would be enough to engage. And, low and behold there was - turning the knob did feel to be driving the switch.
Fortunately at this point, there was no-one else in the house to get blown up with me, so I threw the power on and turned the switch anyway. Still being alive, and the house still having all it's windows, I even braved turning on a tap - water flowed, and it was HOT!!!!. I set the timer up, and the pump whirred, and the radiators started radiating. At this point, the cat wandered in, curled up infront of the kitchen radiator, and looked across with an "about time too" look on it's face. It soon had a "what was that for" look on it's face as my size 8 connected with an appropriate part of it's anatomy.
Hey - I now have a warm house, and a hot shower. And it's all thanks to you. I'm sure I'll forget, and eventually forgive you for making it look oh so easy.
Seriously, thankyou. I'm really happy to have been able to do this myself. I "really" hate paying others to do stuff I can do myself, and especially when the so called regulations say you have to use a "professional" when in fact the professional has way less qualifications and experience than myself, and all the regulations are really doing is protected the commercial interests of the cowboys.
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