Ideal classic se24ff

can be anything from no flame to no fuel etc can try reset or need to have serviced

I sincerely believe that this is reportable to the office of consumer protection. That error is "maintenance alert" and serves to have to pay for it without obligation to check a technical boiler.

the problem may be the thermostat or the heat senser

Do you find that the boiler water pressure drops over time?
Then replace the pressure relief valve. You'll find it in the lower part of the boiler connected to that external pipe.
Close off the water pipes to & from the boiler and then replace
On some you can dismantle the valve and clean the scale from the inside and it works again - but not always 100%
It's either this or the fill tap/valve is not turned off fully

what is the lights doing on the boiler

Combi boilers have many moving parts compared to conventional models so must be serviced annually to prevent breakdowns.

Your boiler most likely has one of four problems:-

1. When the receiver for the wireless thermostat was fitted, other wiring was loosened and has come adrift. It's a possibility, but in my experience unlikely as the wiring involved isn't anything to do with HW supply..

2. During receiver fitting the pcb suffered a static electricity surge. Possible, but unlikely as this sort of damage is usually immediately evident. However, boiler pcb's are notorious for sudden failures anyway and can happen anytime. Combi pcb's are more prone to fail as they usually have up to four solenoids fitted and these do eventually fail due to mechanical wear.

3. When you your combi is in CH mode it heats the primary water circuit and directs the flow through the CH heat exchanger. When you open a hot tap (US=faucet) you're opening a supply of cold water initially as there is no stored hot water like in a conventional system. As the water starts to flow through the combi's diverter valve there's a pressure drop which activates a rubber diaphragm with mechanical connections to other parts. The diaphragm is one part which is routinely replaced annually as it will eventually fatigue and fail with the symptoms which you describe. In addition, the mechanical parts connected to the diaphragm pass through various seals in order to activate at least one micro switch. If the seals fail then the moving parts eventually corrode and seize up. Regular servicing prevents this. Combi seizures are a very common complaint in hard water areas.

4. One of the micro switches activated by the diverter valve has failed. Possible, but not likely. The purpose of the switches is usually to fire up the boiler to provide HW when the CH is not currently running, but as you haven't said which Vaillant you have I can't be definitive on this.

One major problem with combi boilers is that multiple failures can and certainly do occur almost at once. Unmaintained units may appear to be correctly functioning but in reality a number of worn parts can be close to failing. When one part fails, the others can't cope with the stress and fail as well.

In most civilised countries including the UK it's a criminal offence to attempt most repairs yourself unless you're qualified to work on gas appliances, so you need to find a decent heating engineer to service your boiler (ask your new neighbours). In the UK you can expect to pay around £120-£150 annually for a routine boiler service. If the circuit board has failed then it can easily add over £100. If parts inside the diverter valve/manifold have seized then you can be looking at an additional £80-£150. Note that diaphragm failures on their own do not merit diverter/manifold replacement and that if you have a new diverter fitted then a new diaphragm will already be present inside.

Dishonest heating engineers always diagnose a failed pcb as they know that you have no way of knowing whether it's true. If you can live with the problem for a few days then failed pcb's are usually a straightforward repair and there are plenty of companies who will send you a guaranteed exchange unit for much less than the cost of a new one. As long as you are not opening the main boiler casing which houses the combustion chamber and gas valve assemblies then some territories allow non gas qualified replacement, but others insist that the work is done by a qualified electrician: this is not the case in the UK as long as the pcb is not connected directly to mains electricity (no modern domestic ones are).

overheat stat , does it come back on with reset ?best of luck

no but Ideal will post one out to you on request

if the timer is built into the boiler there is a small switch on the right hand side. this can be moved up and down to bring the timer on and off.
if you log onto the ideal web site you should be able to download a copy of the programing instructions.

vailant boilers are one of the best on the market and should last you more than 6 years depending on installation and servicing.
the engineer you had should not have replaced the diverter valve if the boiler was firing up when the taps are opened. if you was getting luke warm water with the boiler alight it is a classic symptom of a blocked plate heat exchanger on the central heating side.
a new heat exchanger can cost around £100 depending on the age and model of the boiler.alteranatively it could be descaled but may clogg again. it would be a good ideal to fit a magna clean filter on the system to help prevent further debris if you have a dirty system .if you don't trust your engineer i suggest you ask another. find out if he is registered first and don't pay until you are satisfied with the work. if you are asking the same engineer back try and get a discount off the work as he has failed to rectifiy the original fault and fitted the wrong part due to wrong diagnostics. if he is registered you can complain to the governing body ie corgi or gas safe register.
good luck.