when was it last serviced? These boilers need regular quality servicing else they will go to an early grave.
I would find someone who knows the boiler well, not any joe bloggs. You could try Glowworm for a fixed price.
I wouldn't recommend any DIY attempts on this, many RGIs struggle to get to grips with them.
sorry can't be more helpful.
mick
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local