no hot water on a baxi combie instant 105e

[sparkyboy14]

i wonder if anyone could help me.i am having a problem with my baxi 105e instant combie boiler.it has no hot water.i have replaced the diaphram in the dhw differential valve as it had a small hole in it.but it was still not allowing hot water.so i changed the micro switch on the front of it but no change.i checked that the pushrod was activating the micro switch,and it is.
i have no fault leds coming on.when its first turned on,it goes through its preheat stage ok.the tap led flashes green.the boiler led is on constant amber.the fan is on.it seems all ok.but when i open a hot tap,the tap led stays green,the boiler kicks up,but after approx 20-30 seconds it shuts down.still no fault lights coming on.the central heating side of the boiler is not affected and works perfectly.if you have any ideas,i would be extremely grateful...
thanks....gary

 

[twgas]

Does it relight after another 30secs or so if you leave the hot tap running?

 

[sparkyboy14]

hi mick
yes it relights after about 30 seconds or so,and also if i turn the tap on more.i forgot to mention that i also took the water filter out and made sure it was clean.could it be the heat exchanger? and if so,whats it like to take it out?and can it be flushed or does it need replacing.
thanks ..gary

 

[twgas]

If, as I believe is happening, the hot water cycles hot, cold, hot, cold, then the most likely problem is the plate heat exchanger has become restricted. This is usually caused by dirt in the system being drawn into the boiler from the rads when the CH is being used. A clean and filter would be a good idea, as well as a clean or replacement plate.

 

[totalservices]

most likely plate but could poss be thermistor worth a try as fairly cheap and from memory are in dry pocket so easy fit