problem with 1deal he24 (1sar)

[bigted]

i have a problem with the above boiler it is 2 years old the guarantee was up in may the central heating works fine. but the other day when i turned the hot water tap on it was only look warm. so when i looked at the boiler the pressure gage was on zero so i bled the system to get the pressure back up.when i turn the hot water tap on with the water running slow it got quite hot for a few min then it went back to warm. when you look on the boiler screen is a letter (d) which has allways been thier.when you first turn the boiler on it counts up to number 4 then the letter (d) comes on the is also a little box on the wall with 3 lights on it when i press the button a green light comes on and the boilewr gets a letter (c) on it and the burner light comes on with the boiler workig. but the hot water is still warm any one got any suggestions.thanks

 

[adlplumbing]

do any other pipes under the boiler get warm

 

[bigted]

yes the 22 mill pipe gets red hot you can not touch it.but after a short time the burner switches off.

 

[adlplumbing]

problem with diaverta i would guess

 

[bigted]

what is a diaverta and what does it do.do you think i have put to much water pressure in when it went down to zero and i adjusted the pressure.