Why is the frost symbol flashing on Neomitis RT1 RF Heating Controls?

Contact a corgi registered gas contractor.

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.

1) Contact baxi:
http://www.baxi.co.uk/contact.htm

2) Which boiler wires? I don't know. Page 24 manual.
Manual says to disconnect link between terminals 1 and 2, and instert timer in-line.
http://www.acwilgar.co.uk/Boiler-Manual-PDF/Baxi/Combi%20instant%2080E%20&%20105E.pdf

2) I can tell you about the timer wiring.
Timer is 230Volts
Not sure if you have British Hot-Neutral 230Volt, or Hot-Hot 230Volt.
Wiring is same 2 wires, but words to describe are different.
Let's say you have Hot-Neutral 230V
Connect Hot to L6
Connect Neutral to N5
This will power the timer so it runs and keeps time.
You can get Hot-Neutral wires from Hot-Neutral that arrive to power the boiler.

Now the timer terminals are separate.
E terminal is Earth or ground.
The Common is Hot wire.
The timer then turns on-off and switches back and forth between DHW and HTG.
HTG is heating
DHW is defrost.
Timer has 2 sets contacts.

When timer activates first set of contacts, then DHW defrost terminal receives power from Hot wire on Com terminal. At this time, all power is cut to HTG heating terminal.

When the defrost cycle ends, then the heating circuit receives power, and then the timer has programming that opens and closes a second set of contacts going to HTG heating terminal.

Which wires from boiler connect to each terminal, I am not sure.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

is the boiler a combi if so have you checked the pressure. it needs to be at 1.5 bar 2 bar at the most . also check that the heat the boiler is producing is completeing the circuit on the heating if you have access to the pipe work there should be 2 or 3 22mm copper pipes. now turn the heating on and check which one is getting warm. the one that is is your flow and in about 2 to 3 min there should be one more pipe getting hot let me no if this is the case

Could be a number of things, none of which can/should be done by homeowner. If unit was installed by a certified P&H installer, call them. They can fuss with warranty stuff and order parts. Also the Potterton Promax HE 24 is same as Baxi.

Can you control heat with thermostat by turning it all the way down. I assume from your description that burner is running. If it is and turning t-stat all the way down made no difference I would remove t-stat from wall and remove red or white wires from it.This should cut power to gas valve turning burner off. If this works replace t-stat. Hope this helps. Thanks.

the gas valve is just a valve that open and shuts which lets the gas in,

the cylinber stat controls the hotwater
there must be a thermsat on the boilet that controls the water temp and a overheatstat thats controls the boile which should shut dow in the event of overheating if you go to the baxi wedsite you can down load the info for your boiler

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.

does the boiler come on when the hot water tap is run if not change the hot water flow switch or the diaphram in the hot water flow valve it may be split