Worcester 28 Combi - No HW, CH ok

[mr_t]

Hi, the boiler is a Worcester 28 Cdi Combi, it seems that the boiler is ok with Central Heating and heats the rads, but there is no hot water, and when the tap is turned on the boiler doesn\\\'t even try to fire. There is tepid water coming out of the hot tap.
Any advice much appreciated!

 

[walkingonsunshine]

It may be the Domestic Hot Water (DHW) sensor, located behind the water to water heat exchanger. It's a flow switch which tells the boiler you have turned the tap on, it should illuminate the DHW demand indicator first.

 

[COG]

The thermistor behind the water/water heat exchanger is just for domestic hot water temp, you will find the flow switch is in the small black box on the end of the diverter valve, when you turn on the tap the diverter valve plunger should come out the end of the valve by around 15mm hitting the micro switch in the black box. Remove the trim panel from under the boiler (if fitted) and look up at the end of the diverter valve (large brass valve) you should see the plunger move when the hot tap is turned on if it does not reach the switch then you either have a drop in mains pressure or you need a new diagphram fitted to the valve.