Central heating working but no hot water

[John1943]

When tap is turned on for hot water only, boiler remains at central heating temperature, rather than reduce to 1 bar as previously. Boiler ia a Saunier Duval.
Any advice? (Retired Plumber).

 

[mikegas]

Apologies if ive read this wrong but bar is a measurement of pressure not temperature

 

[John1943]

Apology is mine! The man of the house was through the other room trying to fix the hot water while I was asking for support on the plumbing forum, (he knows nothing about the internet and I know nothing about plumbing!). Basically the problem appears to be that the central heating is operating as normal, but we have no hot water from the taps.-only cold.
Thanks for replying

 

[Noxer]

Do all your radiators get hot? there could be air in the coil of your cylinder, or your 2/3port might be stuck.

im just a newby trainee, so might want to wait for the plumbers to reply on here.

 

[John1943]

All radiators working as normal, just no hot water at taps. Appears to start up on hot water cycle then cuts out. Thanks for your interest

 

[Noxer]

You got a combi?

 

[tamz]

Diaphragm

 

[John1943]

Yes, Saunier Duval combi.

 

[reqi]

I have the same problem. Is there a solution?? I am looking forward for your replies.

 

[mrr1]

I have a similar issue - I was going to start a new thread but can't suss out how to so I'll piggyback this thread instead.

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.