no hot water but boiler heats up to over 70o c help please

[redminijim]

i wonder if any one could help?
i have a biasi boiler 24s ,its a 2001 model c12 c52.
it was in the house when we moved in and have no instructions.
if we want hot water we have to have the heating turned right up even in the summer !(on the frost setting not the sun setting )
there is one switch on the front that has a sun and a frost sign on it.the sun sign does nothing at all ,does any one know what it is for?

the boiler has been working ok up to a week ago (except for having the heating on in the summer when you want a shower)
but last week we have not been able to get any hot water to have a shower
the symptoms are as follows > turn switch on/heater fires up/ temp guage goes up to 70 o c scoulding hot for 2 secs than cold again .
the flame stays on but no hot water.
i have lived with the other fault for a while now but not getting any hot water is getting me down now.
the heating (radiators all work)
i do know we are on a joint mains and suffer with low pressure but i am not sure if this will be the cause.
i would like some advise really on whether i need a new boiler or it can be fixed , i currently have 5 radiators in the house its a 2 bedroom house if this helps ,how do you go about picking a new boiler if i have to ?

thank you for reading my post ,any advise would be much appreciated jim

 

[ddk]

sounds like your diverter valve is not moving when you open a hot tap. it may only need a replacement diaphragm inside the body of the valve. when you open a hot tap, do you hear and 'clicking' sounds from the boiler? if you do then the chances are the diverter is moving over but the microswitch is not working correctly

 

[redminijim]

hi ddk thanks for reply ,i just tried the tap i had hot water for 10 secs , i didnt here any clicking noise though!

 

[ddk]

sounds to me like your diverter valve needs attention, probably the diaphragm has split

 

[redminijim]

thank you for your quick response i will get hold of a plumber i know and see what he can do cheers mate jim !