Woke up this morning to hot water but no heating. Shoved lever on valve to manual and now appears to be working. No idea how old it is. No previous problems.
Off out to get a new valve. Going on Hol in 4 days for 10 days and in these conditions cannot afford heating failure. Even in Essex it is not all that warm.
Is it best to
a. lock existing valve in manual mode until I return
b. replace head, making sure valve appears fairly free?
Don't really want to drain down system to replace the lot at this point. Usual drain point is outside in the snow!