I bought this only about a year ago, and it has developed a fault. It does not go unless you press down on the chassis over the bogie. Either bogie, but not in the middle.

My guess is this is an issue with the contacts between the bogie and the chassis? However, I cannot get the bogies off to check. Can anyone advise either on bogie removal, or what else it could be?

This is DC, but the model is designed for the next18 DCC chips.

The bogies just pull off. Details do appear in the Dapol Hymek thread. Mentioned here in post 175: https://www.ngaugeforum.co.uk/SMFN/index.php?topic=278.165