Flow Switch

[wildcat2]

Hi,
I've got a Suanier Duval Thema Classic F24 (combi) only a few years old - the damn thing's always going wrong.

Today's problem is a total lack of hot water. The pressure's OK and the central heating's fine. It was working first thing, then just stopped. The water's coming out cold, so obviously whatever triggers the lighting of the hot water part of the boiler isn't doing it's thing.

I've had this a couple of times before but it's fixed itself after a few turns on and off of the tap. this time it looks more serious.

I suspect the flow sensor or the connections to it, has anyone ever dealt with this before? Is it straightforward?

 

[Breesey]

Check diverter valve is operating correctly. The diaphragm may be perished.

Is this what you mean by flow switch?

 

[ChrisR]

It doesn't have a diverter valve with a diaphragm, Breesey.

has anyone ever dealt with this before?

Yes near enough

Is it straightforward?

Now don't be silly, it's a Saunier Duval.

You'll be really glad you asked
It's amazing what you can find when you ask.
I have the manual, so I looked up the diagnostic test, just for you. Ready?

• To test: Use a new detector and
  connect it electrically in place of
  the faulty one .

Easy now, heh?

It's held in with clips and O rings probably with other leak-prone bits in the way. Once out you could try cleaning it and seeing if the paddle wheel spins when you blow through it.
If it's like a similar type I have had in my mitts, you'll get a few volts on the pink wire for zero flow and about 12 v for full flow, when powered up in situ.

Don't consider using any parts list you may have. It may have changed three times. Call SD. Also be prepared for the new bit to look like it doesn't fit.

 

[wildcat2]

There's something the manual refers to as a three way valve, which I take to be the thing you call a diverter, and there's a water flow sensor which I think is what triggers the switching on.

I've now blown the fuse fiddling -oops

 

[Breesey]

It doesn't have a diverter valve with a diaphragm, Breesey.

Three way valve is what I meant. I@ll leave it to you!!

 

[wildcat2]

Thanks Chris,

Sorry for the confusion, you and I posted almost simultaneously before, which is why it looks like I hadn't read your post. I hadn't. Your manual is obviously superior to my crap "owners handbook" which generally features photographs of the bit just next to the bit you are interested in.

I have fixed the fuse (great quote from my nearest DIY shop - "We don't do Milliamps!") - so am at least back where I started, I have identified the flow switch, and checked where I can get one locally. It's about £60 plus VAT so I don't want to get one unless I'm certain this is the problem, although I can't imagine it being much else, except possibly the wiring or the dreaded board.

Obviously I've tried wiggling wires, swearing profusely, and gently tapping with a blunt instrument. I've also cleaned the filter. Nada.

I think I'll whip it off and try the blowing through thingy, but will wait until (a) there's someone else in the house to call the ambulance, and (b) the shops are open in case I need to get a bit in a hurry.

Do you think it IS the flow sensor or am I being diagnostically naive here?

Thanks

 

[wildcat2]

How hilarious, I used a rude word to describe my owners handbook and it's instantly edited itself to "rubbish". What will they think of next?

Sorry if I offended any mods or anything.

 

[wildcat2]

Having pondered further, and been rewarded by a couple of short-lived spurts of hot water, I am now thinking along a different track (sort of).

Could I perhaps not have sufficient flow/pressure to trigger the switch/sensor wotsit. I said that the pressure was OK, meaning that the low pressure warning light wasn't on, but it's not exactly high, hovering a little below 1.5 bar (it's never been any higher, that's all the mains pressure I can get)

 

[Breesey]

Any use to you?


http://www.saunier-duval.co.uk/manuals/pdf/current_products/installation_ThemaF24ePlus.pdf

 

[wildcat2]

Not quite my model, mines the basic, not the plus, but I've backtreacked from there and found the one I need and saved it. Great help already, I thought the manual I had was pretty good, but this is better.

I've discovered that the filter which I carefully cleaned was the central heating one not the hot water filter, so now I can do the right one which has got to be a start.

Thanks a lot, watch this space.

 

[wildcat2]

I've cleaned the filter, which was clean already. No improvement, so I bravely ventured further into the depths. I managed to extract the flow sensor, blew through it and the paddles didn't seem to be moving much, nor did blowing down the pipe with the wires connected trigger the ignition. I took it further apart and cleaned the paddle spindle and replaced it, there was a bit of grit in there. It was better, you could spin the paddles by blowing but they still still stuck every few puffs, so I gave the spindle a little smooth with wire wool, airlined the housing and put a little grease on the spindle and bearing and it seems to be working now. It may die again, but at least I know where to look next time, and it hasn't cost me anything so far.