On 18 Aug, 09:37, Kevin wrote:
Hi all, I have a continuing issue with my central heating system that
is manifesting itself in two ways.

(1) When both my hot water and central heating are on, the boiler (a
potterton suprima 50 litre - 3 years old) bangs and then locks out.
I've had several vists by gas fitters who have recorded the
temperature of the inlet and outlet who state that the boiler flow is
restricted somewhere and the water is boileing in the cast iron heat
exchanger. I've had countless plumbers and heating engineers who have
replaced the circuit boards in the boiler, the flow restriction valve
at the hot water cyclinder, the cold water inlet pipes, the flow
control valve between the heating system and the hot water system etc.
I've also had the system flushed with a chemical cleaner.

(2) Recently my aqualisa power shower is failing to pump water. It
pumps well for the fist 5 minutes and then the water suddely dries up.
You can hear the pump whining but there is no water. Neither cold or
hot. Previously, after showering or running a bath, you could hear the
hot water cylinder being refilled from the cold inlet. Now I cannot
hear that noise.

Well, that's all the information I have. I've spent a lot of money on
sepatate engineers trying to resolve these issues. I was hoping that
someone could give me a few pointers to help me locate what the issue
may be. Otherwise I've a feeling that I'll have to replace the whole
system!

Any advice would be appreciated.

I once attended a boiler with similar symptoms, where the tenant had
closed off "all" the radiators and there was no bypass. When the
cylinder was hot and no path through it there was no flow via the
radiators, the pump ran the boiler fired and the banging started until
the boiler locked out on overheat. Do you by any chance have
thermostatic valves on your system which are shut off or stuck closed?
Ref the shower - check your ball-float valve in the head tank has not
jammed through corrosion or has bebris in the cone resulting in a
dribble only being allowed to enter to replace the run-off.
Final tip get someone competent in who understands what they are
diagnosing.