My flat's immersion heater thermostat has failed and is too long to remove because its top is only 9in directly below the water tank's base. If I get it out (bent) then replace it with a 7in thermostat, will using a long immersion heater with a short thermostat at least be safe? I'd also be very glad to know what heating problems I should expect and/or any other solutions that could avoid disconnecting the tank etc.
Thank you, stoneyboy, for your interest. I think you may be thinking I would use a short immersion heater. I wanted to know the effect of using a short thermostat with a normal long heater.
My long thermostat actually recovered, so I checked the vertical water temperature profile in the cylinder (by systematic heatups and timed runoffs), When no water was being drawn off, I found that the water at the top of the cylinder is about 60 degC and falls steadily down to the thermostat's set temperature (around 37 degC) near the thermostat's sensor. The profile seemed to remain like that indefinately. I was surprised then remembered being told something like that during my apprenticeship.
From all this, I will now expect a short (7 in) thermostat set for about 60 degC to give the same water temperature profile as a long thermostat set for about 37 degC - and the same amount of hot water. The heater will also probably cycle on and off a bit more often. If my long thermostat fails again, I will replace it with a short one and report what I find.