Shower failing to activate DHW (only recently)

[Mathew J. Newton]

Hi everyone,

I believe I've got a problem with either my boiler (Worcester-Bosch

24CDi) or shower (Mira Excel thermostatic) and as a result of my investigations I *think* I'm close to solving it... however I'd like your input before I go further...

I fitted my shower a couple of showers and have, until recently, been more than impressed with it's performance. Whilst my boiler can only supply 9.5l of hot water this has been sufficient to provide excellent performance from the Excel. Indeed, boiler performance all round (DHW and CH) has been great.

However, the other day the shower was somewhat erratic in that it kept fluctuating between hot and cold. Investigation of the boiler, whilst the shower was running, revealed that the DHW light occasionally turning off. Upon a more detailed inspection/testing I could see that the plunger on the diverter assembly was not always depressing the microswitch (DHW flow detection) - occasionaly it would retract slightly from the fully out position thus making the switch open circuit.

I thus assumed that the shower was perhaps not demanding enough hot water (I should point out that the shower was on quite a hot setting so it should have been) and indeed turning a hot tap on, whilst showering, appeared to 'solve' the problem. But why? Particularly as it's been running fine for two years.

Well, I dismantled the shower body and immediately noticed that the inlet strainer on the hot side was almost completely blocked with what I can only describe as 'black stuff'. I couldn't work out whether it was plastic or what - looked like granules of ground plastic or dirt. Anyway, I cleared this and reassembled. Shower slightly more powerful (could be in my mind?) but the DHW demand assembly is still not remaining on. I did read somewhere that the Excel can keep up performance with a 50% blockage so I wasn't entirely confident that this would do the trick to be honest.

I took a step back and wondered what on earth this 'black stuff' in the strainer was, particularly as the cold side was completely clear. I'd expected to find limescale but not a trace (on either).

Here's my question (finally!) - do you think this 'black stuff' could be the result of a decaying/perishing/whatever-ing diaprahgm? Does this happen? Sure, the boiler runs continuously if a hot tap is held 'wide' open so the diapragm can't be *completely* shot (at least *yet) but could it be on its way out?

I must admit to not knowing exactly how these diaphragms work (that might help!) but I'm guessing it's got holes in that allow the water through, but with sufficient drag to move it (and in turn depress the microswitch indicating demand). Can just this diapragm but replaced (do they fail?), or is it a whole-diverter-valve affair? Or indeed something else?

All help/opinions most welcome, and sorry for the long post but I wanted to included everything.

Cheers,

Mathew

[Mathew J. Newton]

Any boiler experts out there....?

Mathew

[Mathew J. Newton]

I guess not! ;-)

For the sake of the archives in case anyone else has symptoms of this nature (see thread for details), I can confirm that my problem was indeed down to a perished diverter valve diaphragm as can be seen (old and new) at:

my luck that having never previously taken a boiler apart (I didn't know how combi's worked until last week), the diverter valve was only accessible once the filling loop, water-to-water heat exchanger, manifold, bypass and pump connections have been removed! Still, if nothing else I've learnt a lot in the process and not to mention the saving I've made by DIYing it - I'm sure if I'd got a pro in then not only would the labour rates have been quite high but I bet they would have replaced the entire diverter (£60+VAT compared with £15+VAT for the diaphragm) but would they also have replaced all the o-rings, fibre washers etc as per best practice? Perhaps I'm being unfair...

Anyway, enough of my rambling - I'm off to sup a can of beer whilst sweating in front of the radiators... despite the sunny weather one has to give the boiler a thorough run-in, if only as celebration of the job!

Mathew