viessmann boiler trouble

[phill7530]

can anyone help. I have a viessmann vitodens 100 boiler, 35kw, and the hot water does not work properly. the central heating works fine and the tap symbol come on when you turn the tap on. the pressure on the gauge is at 1.6. sometimes you turn the tap on and it will fire up for s few seconds and the water gets hot and then it shuts off and will not restart. any ideas? it is type wb1b.

 

[holty]

when you turn the tap on. look at the display what temp does it reach? your probably gonna say 80+ though.

 

[phill7530]

Not necessarily, sometimes temp will be 50 or 60. It will run hot at the tap for a short while then you will see the temp in the display start to drop and it will go cold at the tap because it has switched the burner off. The flame symbol goes off.

 

[holty]

well rules out what i thought. so back to questions... is your tap on a constant good flow? eg if you leave it on dose the flow of water from the tap diminish? is this a problem on all the hot outlets?

 

[phill7530]

The bath tap does get hot sometimes but the two taps in the kitchen just about never get hot. The flow doesn't decrease but ots not as fast as I would expect nor is the pressure.

 

[holty]

when you run a hot tap. and after the burner symbol has gone out. does the tap symbol still stay on. best have ch demand for this.

 

[phill7530]

Will check tomorrow and let you know. What does ch mean?

 

[phill7530]

Checked the temperature in the display, 19 degrees. Turned the hot tap on and the tap symbol did not come on. I switched the boiler off thenbon again and it woke up for about 15 seconds, the tap symbol came on but the burner did not kick in, aand then it shut off again.