The A01 fault code is nearly always down to the pcb, 99% of the time in fact, its a common fault, but not common enough for ariston to be responsible for boilers out of the warantee. you can normaly check this yourself, while the tap is running check if the electrodes are still sparking even after the gas had lit, this means the pcb is not detecting the flame and trying to relight. eventualy it will lock out with a A01 code, if u reset it might work for a short time but eventualy u will get to the stage where it will no longer resart.
if your handy you can replace the pcb yourself, there is someone selling them on ebay for £85 thats a steel, its half the trade price never mind retail price!
pcb part number is 65103422 just search it on ebay!
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Does the red status led in the centre of the control board come on when hot water is drawn? You need to remove ONLY the front decorative cover to see the control board, two fixing screws at the base of it. If not the boiler won't fire when the CH is off. The trigger for this is a pressure switch, replacement of which is beyond DIY scope. FYV
odd noise like popping or singeing fire....clicking noises.....sounds like you have a water leak putting out the pilot.......or your thermo coupling is bad....or the noise is the tank full of calcium buildup and that will make noises when the burner is on
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).
If it has a distance from the boiler to your use the water in the lines and the lines themselves ahve to warm up before you will get hot water, Let me know more if this dosnt help. Please rate me as high as possible if it does help you understand your trouble.