Their wording when it comes to refunds is rather weaselly, and at odds with most of the rail industry. For delays, they offer refunds if you're delayed over 15 minutes, but with a huge number of exclusions:
Originally Posted by Hex
1. line closures at the request of the police or emergency services;
2. acts or threats of vandalism or terrorism;
3. suicides or accidents to trespassers;
4. exceptionally severe weather conditions;
5. gas leaks or fires in lineside buildings not caused by ourselves or any of our employees or
agents;
6. fire or mechanical failure due to electrical failure or a defect (except where this is caused by us or
our agents, or as a result of the condition of our trains;
7. railway infrastructure failures
8. industrial action, riots or civil commotion;
9. acts of war (whether declared or not) or acts of god.
So, in this case, you'd be excluded.
OTOH, they will give discretionary refunds with a "reasonable" processing fee of "up to" £10. What this means in practice for lengthy cancellations, I don't know.
All details are in the CoC:
https://www.heathrowexpress.com/File...ge-May2012.pdf