On Fri, 23 Nov 2007 04:57:19 -0800, stephen.travis wrote:

I have had a loft conversion on a two-storey house, now three storey. As
part of the conversion the hot-water system was changed from non-
pressurised to pressurised. The new cylinder and associated pressure
vessels were re-sited in the loft. The top storey radiators are run off
a separate control system.

Since installation of the new system (last August), I have had continual
problems with the boiler over-heating and cutting out, usually after
around 30 minutes but sometimes even more frequently than that. The
builder has had his heating subbies back many times and they have done
the following (allegedly):

- replaced the mother board on the boiler - drained and cleaned the
radiator system - installed an additional pump in series

None of it has made any difference.

The boiler is a Baxi Solo 3 PFL 70. On the ground floor there are 5
rads, 7 on the first floor and 3 on the second floor.

Finally a different heating engineer came round and diagnosed the
following:

- boiler too small for the new environment - flow pipes from boiler to
tank should be 28mm, rather than 22mm (replacing these would involve
major work ripping out stud walls in the newly finished conversion)

When this information was presented to the builder he indicated that
this was rubbish and that only a new boiler was required, as it wasn't
powerful enough. However, surely a weak boiler would just take longer
to heat up the rads?

On the advice of a friend I de-synchronised the hot water and central
heating. This cured the problem for about a week; then the boiler began
cutting out again on the hot water phase, and now is cutting out again
on the heating phase.

I do not want to have to buy a new boiler if its a simple problem - two
suggested faults are a new thermostat and a faulty bypass valve.

Any suggestions as to the likely cause of the problem, or what to do
next???

Many thanks!

Almost certainly the CAUSE of the over heating is a lack of primary flow.
This is not likely to be the boiler, pump(s) or mother board. The buggers
should have cleaned the system out when they worked on it, anyway we can
assume that has been done.

My guess is that the control system is wrong. You sound like you need
something like a 3 zone extended S-plan controls.

If you are electrically competent make a complete wiring diagram of the
heating control system. You might also have a pipework routing fault but
seeing as the system does work some of the time perhaps not.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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