Hot radiators but no hot water!

[safetyman]

Suddenly my boiler has decided that it won't heat the hot water in my cylinder. But the central heating works fine. If I leave this on long enough, the hot water does heat up a bit, but nowhere near the temperature it should be.

The immersion heater doesn't appear to be working either.

Any help would be greatly appreciated.

Mark

 

[MANDATE]

From what you say, I assume you have a motorised valve which can be in any of three positions, ie( hot water) ( 1/2 hot water1/2 heating) (heating)
You may find the spindle has a little resistance and is stuck on heating or the mid position.
There should be a lever on the side of the valve that you can latch it or lock it to one side.
With electric off you may be able to remove the motor and turn the spindle by hand.( A little WD 40 will help)
Dont forget to unlatch the lever afterwards.
Regarding immersion heater, first establish if cables going to and leaving swich is live .
With electric off and cover removed use a continuity meter to see if there is a continous path through the element and through the thermostat.

 

[ChrisR]

Most 3 way valves spring-return to the hot water position, so it's not likely to be one of those, though they can stick. If it has, give it a whack with a large screwdriver handle - or unscrew the fixing screws a little. More likely that there are 2 "2 port" ie one in one out valves, and the one for the hot water is dud. If the things are by the HW cylinder follow the pipes to find the right one - on a pipe which goes into the cylinder part way up.

Opening the valve manually won't help a lot, though the HW will then heat up while the CH is on. The fault is usually the motor in the valve head which can often be changed (£15 or so in Wickes etc), though the mechanics of the head can pack up - £35 or so I think.

Some types / makes are a pain - you have to change the whole valve. Give us some details