"Ed Sirett" wrote in message
news
On Sun, 19 Mar 2006 04:57:54 -0800, Giggler wrote:

We have an old Celtic FF boiler which is no longer heating water.

The heating system is fine but when you turn the hot water tap on the
boiler no longer switches on. When the heating is on and you turn on
the tap the boiler turns off.

Just to make sure that I'm not barking up the wrong tree...

This is a typical budget style Combi boiler by Chaffoteaux.

If you had not said that the heating is turned off by running a tap I
would have said the most likely cause is the diaphragm on the DHW side.
It might still be that.

Likely

Either: the diverter valve is moving just fine and the micro-switch that
tells the boiler to do HW has failed. Or: the diverter valve is not being
moved quite enough to make the microswitch operate but is being moved
enough that the flow to the rads is cut (which then causes the boiler to
turn off due to it's internal thermostat).

The spares required for this are probably a microswitch and/or a diaphragm
and some inhibitor. Less than half a day to fix if all goes well, and
assuming this diagnosis is correct.


IIRC the diverter valve has a black casing containing two microswitches
mounted on the end of the operated shaft. The factory fitted switches are
not especially robust so I used to use a higher current rated type when
renewing them. A couple of these switches will be only in the order of a
fiver and its a trivial job to swap them as long as you ensure they remain
in place as you refit the casing lid.