hot water problems

[carljb]

I have a worcester 240 combi boiler. I have hot water when the tap is turned on slightly but when i increase the flow i loose the water temperature even though the burner remains ignited.
Ihave also noticed black bits and a vibrating noise when the hot tap is turned on. Could these be connected?
I would be grateful for any advice
thanks

 

[compheat]

The black bits and vibration could just be the tap washer disintergrating. the hot water temp might be down to a faulty thermistor (this is what maintains the temp)

 

[carljb]

thanks.I`ll check it out

 

[carljb]

I`ve changed the tap washer but still get vibrating noise(more like a light aircraft)when either upstairs or downstairs hot watertaps are turned on.
Regarding the thermistor is there another name for it ? There is no mention of it in my manual
Black bits have vanished.
THANKS

 

[mcguire]

Hi. If you let the central heating go cold. I mean realy cold. Turn on the tap without central heating on. feel the CH flow pipe on the boiler. if this gets hot then the diverter valve will want swopping as the hot water will be passing down the heating circuit. This will be why the burner remains alight without the HW getting hot. Check this then let me know.

 

[carljb]

Followed advice.
When hot water turned on fully (sometimes get hot water) CH flow pipe warms up slightly when HW turned off CH flowpipe becomes very hot for about 10 secs.
When HW turned on and temp remains tepid or when washing machine calls for hot water CH flowpipe becomes very hot.
THANKS in advance for any advice