Biasi 24s - Boiler fires and runs on C/H when controls are not asking for heat, timer is off, room stat is off, just power to boiler,seems to be cotrolled by Hot water potentiometer.

Call for Service. The timer is fine, the boiler has failed. I presume it is gas fired, which means that only gas registered service techs can work on it.

Isconnect from the hive ,it has been known the hive thrmostat fails on ideal boilers.

Check thermostat since unit is working but is shutting off prematurely.

check pump is running ok..if not replace it the pump, if pump is ok then u will need to descale boiler put in system by rad or if not combi then put in open vent tank make shure its the small tank also make shure the valve in tank is not stuck

It not wired in right that why its coming on when it is off The boiler is over riding the programmer when it is off .
The boiler should call for heat if programme is on it sounds like boiler is wired into the 24hr mode or over ride mode that why it is coming on . google wiring for y plan heating system. this will help you fault find on this . changing vales and thermostats will not help you . Hope this helps .

change stat

back boiler run from a gas fire? check the instructions to operate the gas heat to the back boiler not just the fire
I presume that this a fully pumped system - air lock doubtful There maybe on/off valves on the pipes to and from the back boiler [situate close to cylinder] make sure they are on - anticlockwise turn
or there could be a blockage in the outlet from header tank usually in the loft. or If there is no water in it maybe the mains cold feed it is off.
Note if no water in it DO NOT USE the back boiler

I couldn't find the exact match for your boiler but I have included the website for you. Since you have the product right there, you will probably have better luck. If you can't find what you need, then use the contact info and give them a ring.

http://www.biasi.co.uk/frameset_acro.htm

check to see the time clock is set with the clock symbol. there are three settings on analog clocks I , O and clock the I setting is constant running, the O setting is off and the clock setting is timer.
also try setting the thermostat up higher to see if the boiler fires.

Prior to writing the above fault I had asked the owner to turn the boiler temp controller , for the heating side, down just a fraction . I was phoned this morning to tell me that the boiler had stayed on allnight with no fault light . After consulting with the plumber who fitted the system it appears that there might not be a room stat ,