Probably the flow detector needs a service. It's supposed to be
checked and the actuator greased annually. The flow detectors can
start leaking water, and get cruded up with hard water scale too.
Don't try to force it to light -- if it does, it might fail to
shut the burner off when the water flow stops, and depending on
the age of the unit, that will destroy the whole water heater,
and possibly other plumbing in the house, see
OTOH, if the Thames is the electronic one with full thermostatic
control (and I can't remember which model is which now), then it
might be related to the electronics.
Get a CORGI engineer in to service it, and be thankful the burner
stuck off and not on ;-).
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.