You can use one of these to check for a magnetic field - didn't have a solenoid to hand but picks up the transformer in the charger:
Available from here
(All it consists of is a reed switch, resistor, LED and a battery - if you are feeling inventive you can make your own)
.........New valve is the best and most reliable repair.
......... you bin it and get a new one
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.
Are you a trade or supplier? You can create your listing free at DIYnot Local