DIY Doctor UK DIY Forums

We have a Alpha Combi HE CB33 boiler which has recently started to fail to heat the hot water. Sometimes you turn on the hot tap full and no hot water comes out even after running for 30 seconds. Sometimes it is hot as normal as soon as the boiler kicks in. On one occasion the hot water cut out mid-shower.

Any ideas what could be wrong?

Many thanks
Hugh

Probably a problem with the diverter, maybe the diaphragm is split or stretched.

Do you find if it only happens at certain times of the day, they tend not to work when there's a greater demand on the MCWS, first thing on a morning before when people are showering etc before going to work and again in the evening. As there's not enough pressure to make the connection with the microswitch.


htg

Thanks for your reply.

It does seem to be worse in the morning when the central heating is also on?

Any idea of how much it should cost (parts + how long) to fit a diverter value or diaphram? Can the diverter value be repaired (new washers) or should it be replaced?

Thanks alot

Hugh

It seems to be worse when the heating is on. In the morning the heating is on and we really notice the problem (hot water not kicking in).

If it is diverter value issue or diaphram can they be repaired or just replaced.

Any idea of costs of parts for either or fitting times?

Many thanks,

Hugh

The diaphragm can normally be replaced, should be able to get them for under £20.

htg

My Gloworm Combi seems to have a similar problem. It is quite randomly deciding not to fire up and heat the hot water when the hot tap/shower is switched on.

It seems to be related to the flow rate on demand. At its worst - we have to turn on the kitchen tap (with the greatest flow) to get the boiler started, then quickly switch on the required tap/shower to keep it going.

It seems to need more flow rate to get it going than it used to?

Any ideas/solutions? cheers

As above - diaphragm kit required (more than likely).

htg