Baxi 3 Solo Boiler will not ignite

If the thermostat wire run passes anywhere through, beside or inside any metal surfaces and the wires touch any of the metal its the same as if you turn the stat to on. I've seen this a few times. Easiet way to detect it, if its inside the house is at night in the dark. Look around when its doing this you may see the small spark when it goes on. Otherwise you will need to inspect the entire run from the stat to the untis, etc.

Overheat Thermostat or thermostat sensor...

I am attaching the pdf document I found
(diagram on Page 30, items 16 & 17)...

http://www.freeboilermanuals.com/assets/pdf/baxi_disc/SOLO%203%20%2030-80PF%20SYSTEM.pdf

Several options... (most likely 71 & 72 ... Page 44)

Either unit could be defective... or legitimately REACTING
to a PUMP or FAN failure...
(or faulty wire to the control board)

The "LOGIC" on your control board is looking
specific temperature within a MINUTE...

Failing to see the Overheat Thermostat or
thermostat sensor... in a specific state ... the logic
will cut the fuel...

The "MANUAL" includes a trouble finding guide
(APPROXIMATELY after PAGE 44)...

Save the SWAPPED OUT PARTS AS GOOD SPARES
and buy yourself SPARE "sensors" so they will never
fail again).

Hope this helps.

Carnac the Magnificent

F04 is a fume thermostat fault

The color code for thermostat wiring is as follows.
The "R" terminal is power into the stat from the boiler control transformer. Normally 24 volts. The "Y" terminal is for cooling. Normally left blank for a boiler. The "W" terminal is for heat. This one used to start the heating cycle.The "G" terminal is for fan operation. Probably not used for a boiler. Check the boiler terminal board for these functions and write down the wire color on each one. Match the boiler colors to the right function on the stat. If you need more than this, let me know.

This does not sound like a thermostat problem. I would be looking for a zone valve or circulator pump problem.

there should be a switch which toggles between hot water only /// hot water + central heating /// & possible off on
Either on the boiler or on a separate timer control

this will be your diaphram inside your divertor valve.
the one that looks like a spaceship.
it will e split.

if you have hot water at the taps but the heating isn't working make sure the thermostat is set high enough for the boiler to run check the time clock settings are on.
if these are working it could be a faulty diverter valve switch not sending a signal to the boiler to run.

it was a faulty heating pump. replaced, all ok now.

baxi boiler relief valve blows off when heat is turned on when hot water is working it is fine