Minimal hot water from Vaillant Combi Boiler

[roddamm]

Hoping to catch the eye of a central heating engineer or DIY-savvy person out there...

Our boiler has been working fine for all the time we've lived in this house (4 years) and was apparently new(ish) when we moved in. But all of a sudden the hot water from the taps has stopped. Water comes out and will be (reasonably) hot as long as you run the tap at a trickle - turn the tap on some more and the water comes out faster but becomes luke-warm, turn it up some more and it's stone-cold. The strange thing is that the radiators are still blazing hot. We haven't changed any settings or turned on any more radiators, it just seems to have gone...

Any ideas before I call out an engineer?

Many thanks in advance.

P.S. if you need any more info (like boiler model number etc) I'll be here and waiting

EDIT: My apologies, having seen some similar topics after I posted this, other people seem to have had the same problem... Can anyone confirm if this sounds like a new diaphragm is needed? I checked the boiler and it is a Vaillent TurboMAX VUW GB 282/2-5.

 

[roddamm]

Someone else has suggested it could be the heat exchanger scaled-up...

 

[pompeyal]

I have had this problem with several boilers and most times the diaphram has been the culprit, but have had another instance that the in-line restrictor has been at fault. I would look toward the diaphram in the first instance, you can get the kit from the boiler section at most plumb centres for a few quid and are not too difficult but a bit awkward to install.

 

[nikon70]

scaled up mostly )

not sure about the diaphram

 

[mickyg]

Let the heating go cold. Run the tap and feel the heating pipe from the boiler, if it gets hot, the diverter valve is faulty. If it stays cool then the plate heat exchanger is probably full of carp or scale. My moneys on the plate he

 

[roddamm]

Thanks for all the suggestions. I'll give that last one a go. Looks to be heading towards the heat exchanger though. I had a look at the boiler and it's at the back behind a lot of pipe-work. I bet it's gonna be an expensive job

 

[mickyg]

its a 30min job, and thats being generous.