Saunier Duval hot water probs.

[joe-90]

Hi folks, the GF has got a Saunier Duval Thema F23e and she reckons that it has lost most of its hot water today. If she runs the tap when the heating is on she gets a couple of seconds of hot water then it runs luke warm again. The fact that it runs hot initially suggest (to me) that there is hot water at the plate heat exchanger so I'm guessing that it must be something to do with the reversing valve. When I nip over tomorrow I'll let the system go cold and then let the hot water run whilst holding the pipe out to the rads. If warm water is going to the rads then would that suggest I'm on the right track?
Looking at the flow chart, it seems to suggest that there is a diaphragm that needs replacing in the reversing valve. If not that it says replace the dhw microswitch. And if not that then the thermistor. I reckon I could replace the thermistor and the microswitch okay but not too confident about the diaphragm, so I'll likely get someone in or I'll be farting about for days. So all I really want to know is: which of those is it likely to be? Cheers folks.

 

[ianmcd]

Most likely the diaphragm and not too bad a job to someone who has done one before but a bit of a job for a first timer Im afraid

 

[joe-90]

Yes i agree, I won't attempt the diaphragm.

 

[Andygasman2010]

It's the diaphragm. I think this is the one...

http://www.allsparesdirect.co.uk/index.php?main_page=product_info&cPath=31_199&products_id=3493

But check before you buy it.

It doesn't have a plate heat exchanger, I'm pretty sure it's a duel-pass/flow.

It's warm initially because it's picking up heat from the heat exchanger when the heating is on.

 

[joe-90]

Thanks for that. The houses near the GF all have the same boilers and the same local guy seems to fix them all so we'll give him a call.