Leak from boiler only when CH is on

[boredbrain]

Hiya, was hoping for some help, we have the Ideal Isar HE30, roughly 5 yrs old, that's started showing an L9 fault and we have no hot water or heating, the pressure was low so I sorted that out and it worked fine for a little bit but then went off again, again with the l9 fault code showing, but this time water leaked from the bottom of the unit, the leak didn't last long and I turned it all off over night and checked again this morning and no more water so I fired it up again and after about 10 minutes of firing the CH the drips started again and the pressure started to climb, turned it to hot water only and its fine, pressure is back to normal and theres no leak. I don't understand why the leak and pressure climb happens when the CH is on but not when the hot water is on.

Any clues guys?

 

[mpheating]

I would check the expansion vessel is charged with air, common fault. If this was to fail your pressure would hit 3 bar and it would open the prv valve and dump the water outside. (I know you say under boiler but perhaps loose connection on prv)

Second thing I would check is auto air vent in boiler is not leaking, I think its at the very top at the back right side.

Third thing I have come across is leaking heat exchanger that has perhaps made itself up, I went to an isar today and the connections from the heat exchanger were all crusty...

Your best bet would be to call in an engineer so he can check a few things out for you.

PS: Crap boiler