No DHW from my Baxi Combi Instant 105HE - Help!

[StevenG]

I'd be very grateful for some advice.
I have a Baxi Combi Instant 105 HE and today it gave up supplying domestic hot water. The CH circuit is pumping away fine. When I turn the DHW taps on, it just flows cold. The boiler recognises the demand and the tap icon lights and the boiler fires but no hot water! I've taken the Diverter Valve Operating Head off and it is getting power and operating when CH is demanded (Pin fully extended in DVOH) - seems to draw back in when only DHW is demanded - anyway def getting power. Not sure what to try next - could it be the DHW temp sensor? Could it be a diaghram? If so, which one?
Help!! I replaced the entire Diverter Valve assembly earlier this year so cannot see the valve being stuck. Also drained and flushed the entire sysytem about 2 months ago and it was very clean indeed.

 

[maxil]

Hi had same problem my nephew is a plumber told me it was probably the diaphragm got one for £8.70. When my nephew took old one off had a tear along the edge took him about 10 minutes to replace it working fine now. Hope this helps!

 

[StevenG]

Thanks maxil
I've taken the microswitch off and the push rod has a good resistance when pushed in and pops out immediately when released which makes me think the diaphragm is OK. Not a hard job to take it off and have a look though. I've tried testing everything I can and all seems to work as it should - it just doesn't deliver any hot water. This has left me thinking that it is my shiny new diverter valve that is at fault - it's the only thing left. I assume that if the DHW temp sensor was at fault, it would over heat the hot water rather than not heat it at all.
I will check the diaphragm tonight.
Cheers
Steven

 

[bellairaphon]

does the phex get hot? is the diverter head coming out when hot water selected?

Nath

 

[StevenG]

Hi Nath
With the Diverter Valve Operating Head spring clip removed, the head only seems to rise when CH is demanded. It does not rise when DHW is demanded, although the tap icon lights and the boiler fires. The Plate Heat Exchanger does not get hot at all. I've found that if I run the hot water very slowly, I do get hot water and I suspect that the diverter valve is acting as a heat exchanger.
Steven

 

[StevenG]

Nath
In case I misunderstood your question - The vertical push rod in the diverter valve does seem to rise when DHW is demanded but there is little resistance in it when pushed. I was going to attempt to pull this rod up but cannot really get a good grip on it whilst it is in situ. I did get a tiny pair of grips on it but it doesn't seem to want to come up any further.
Steven