Firebird C20 70K Combi Boiler no DHW

[Bohica41]

I have an old oil-fired Firebird C20 70K combi boiler, that provides CH and DHW to my house which has a single bathroom with sink, shower and bath. Lately the pressure and volume of the HW has been pretty risible...with literally just a dribble of water coming out - although the boiler fires up fine and there is no lock-out. Now this piddling flow has effectively stopped and there is no DHW at all. Indeed, in the upstairs bathroom there is definite hammering if the HW tap is turned on (although no hammering if the bath taps are run...but then, no water either. The CH seems to work fine (so I am assuming that the problem is not with the heat exchanger in the boiler?). I have read other posts/threads which spoke of issues with diverters/diaphragms and sensing switches - given my 'symptoms' are there any engineers out there who could enlighten me - before I make the 'dreaded' call. And, before you all rush-in we are awaiting planning permission for an extension that will also include the removal of the combi and replacement with a sealed/unvented system, for which the cylinder and boiler have already been bought - if onlty the damn thing could have held-on for another couple of months.

In anticipation Many Thanks

Sam

 

[WHPES]

Are you in a hard water area? Sounds like the heat exchanger is due for descaling. Otherwise it may be a mixing valve problem.

 

[Bohica41]

Thanks for the swift response. Is the heat exchanger an item that I could reasonably remove myself, or descale in situ. Having just had a further look at the boiler and the manifold coming from it, the DHW pipes are scolding hot - but there is just no appreciable flow rate coming through the taps. Does this concur with your theory about the heat exchanger? Also the heat exchanger visible at the front of the boiler was hot to the touch at the top - but cool at the bottom. Again, not sure if this information is relevant, but just trying to give you a full picture.
Regarding the mixing valve - if this were the problem is it simply a one-for-one swapout, or is there further testing/remedial work that can be done to it.

Sorry it's a alot of questions - but I have a wife who is starting to complain (and slightly whiff)

Cheers

Sam

Forgot to add that I'm in South Oxfordshire - which I believe is a hard water area.

Sam

 

[peteh20]

definatly plate heat exchanger the boiler should be fitted with iso valves onto the rest of the heatingso easy to isolate and shut down. Have never descaled one only replace them but you will need to address the hard water problem with a scale reducer