saunier duval - central heating but dodgy hot water

[mrr1]

My SD combi (Semia Condens I think) is almost 5 years old. Through most of the year everything is great. Over the past couple of winters its started playing up. When you open a hot tap you've got to open the tap almost fully before the system senses flow and fires the boiler up. It seems that the colder the weather the more pronounced this gets. When the boiler does kick in the hot water is only really tepid - not hot. For the past few days I've had to dial up the CH thermostat a degree or two so the central heating kicks in. When that happens the boiler kicks in again and I can get as much hot water as I like out the taps - scalding hot too!

I'm wondering if theres a flow sensor that looks for signs of hot water tap flow thats simply being a bit stubborn? As I say when the boiler is heating the CH water the tap water is lovely and hot but without the CH in operation all I get is lukewarm water and even then I've got to almost fully open the hot tap before the boiler "clicks in". The boiler is next to a sink so its not hard to open / shut the hot tap and listen out / watch for different things.

Any advice greatly appreciated.

 

[Billy Bob Bob]

you have a diverter valve problem

 

[mrr1]

cheers

gasman

whats a "diverter valve" and what does it do?

 

[mrr1]

also - another question - would the DV change how much the hot water tap needs to be turned on to bring the boiler into action? Sorry for asking so many questions - just that money things are really tight and I want to be doubly sure before I start trying to fix things.....

cheers

 

[Billy Bob Bob]

it diverts water around a plate heat exchanger and creates hot water,when it fails users can normally get hot water with the heating on probably a nightmare to replace on a saunier duval

 

[mrr1]

incidentally if theres a boiler engineer in the s****horpe region who fancies a bit of a sunday job I can very easily pay in copious amounts of Sentinel x100 / 200 / 300 / 400 etc.....

 

[mrr1]

gas man - you're a star!

Just taken the head off the diverter housing - the retaining clip was wet and corroded and just snapped - you can plainly see the diaphragm rod only touches the microswitch when the waters on full blast. I've ordered a diaphragm kit - all I need to know now is how do I fit it?

Other than isolating the boiler and cold water infeed what else do I need to shut down / turn off?

(looks a bit of a b**ch, mind, about eight screws around the diverter housing with no obvious way to get to then straight on)