Hi,

I really hope you can help me because this problem is driving me nuts!
There is something wrong with our heating system which is causing it to
just do random things. Sometimes it won't turn on and other times it
won't turn off (this morning is a prime example of that). At other
times it will come on maybe for a few minutes and that just turn itself
off.

I come to you in desperation. There is such a shortage of plumbers in
this area that they won't come out unless I can reproduce the fault
while they are here but the fault is random happening for maybe a day a
week. I did manage to talk to one plumber who thought it might be the
circuit board in the boiler (the boiler is a Glow Worm Space Saver 50
MkII and looks quiet old) but I am really sceptical.

Anyway a few more details. The most dangerous thing that happens, IMHO
(please excuse the fact I don't know what all the various bits are
called), is when the boiler fires up but the hot water produced is not
pumped around the hot water tank or the radiators (the pump goes ten to
the dozen and sounds like it's trying to tear itself off the pipe). I
am fairly sure there must be a safety cut off because under those
circumstances the boiler does go off briefly. The Honeywell controller
/ timer box, an ST6400C (http://www.plumbworld.co.uk/acb-1357), has
been bodged on to the wall (previous owners fault) and tapping it, even
very lightly, with my finger can cause the heating or hot water to come
on.

If I had to make a guess I would say that it is the controller / timer
box but I don't know for sure. Any ideas?

Bearing in mind our boiler is quite old I would also be interested to
know how if you think it might be worth ripping it our and sticking in
an instant heat system (or heat on demand)? At some point the house has
had a loft conversion so it has no header tank - it has some
complicated Megaflow thing-m-bob with a little red pressure tank
instead. Removing the hot water tank would give us a lot more storage
space so it is an option if repairing the existing system is going to
be very expensive.
Many thanks for getting this far down my rambling post )