Does anyone know of a way to get a temperature reading from an unvented indirect hot water cylinder (tank)? I have a Megaflo for my home hot water system but I haven't found a way of reading the water temperature. The cylinder does have an electric heating element but we use the gas boiler to heat the water as it is more economical.
My use case is that I want to know when we run out of hot water so I can start the boiler to reheat the cylinder. I run the boiler on predefined schedules for our hot water needs and this works fine most of the time. Occasionaly we may have visitors or some members of the family (usually suspects!) will have longer baths or bath too close to each other and deplete the cylinder of hot water. So while this doesn't happen too often it is still annoying when it happens specially since unvented cylinders don't give much warning when they are about to run out of hot water, one minute you have hot water and the next you get cold. This is because the hot water outlet is at the top of the cylinder and the cold inlet at the bottom and as you already know cold water moves to the bottom and hot to the top so you get a strong thermocline effect. I guess I could try to connect to the electric heating element relay but I suspect this is not what I want. The relay will probably just be On when the water tank is below a certain max temperture (which you set in the cylinder) and Off when it reaches it whereas what I want is to know when the cylinder reaches a Min temperture I will define. Thanks!