I think you will have to bite the bullet and call in a heating engineer or similar to look at.
If the part is faulty and has a date stamp on the part (they usually do inside) or you can show the invoice/receipt from the original installer, the part can normally be replaced free of charge from the likes of Heat Merchants or similar. Depending on who you call in and what their relationship is with their supplier, they may or may not replace the part foc. I know if I bring a faulty part to my supplier even if they did not sell it, they will replace it foc if they deal with that particular manufacturer.
The labour for replacing the part will not be covered by the manufacturer or the supplier. You will have to pay for this yourself.
BTW check the zone valves. They are normally the culprit. They are also the main component that actually calls in the boiler. If a zone valve is at fault, you will only require the new actuator head part of the valve. This can be unscrewed and replaced very easily. All wiring is colour coded. Manual for Honeywell S plan is and for Y plan is