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Since being home noticed the hot water is boiling hot, am assuming the thermostat has gone bung so ?? do we get it fixed OR go for Solar hot water system.. (the hot water heating is off peak rate so not a huge cost)

Go solar free from the sun ?

Have you filled the tank Dot ? Ease the safety valve open till water runs out the overflow, what has happened is that most of the water in the tank has evaporated so when the element comes on it overheats what is left quickly, when the tank is full this does not happen.
William
PS be careful the overflow water will be HOT !!

Don't go solar if you are thinking of selling, just get a similar heater.

Dot the HWS should have a tempering valve on it, maybe this will be the culprit?
It shouldn't let water hotter than 50 degrees through to you -except perhaps the kitchen sink??
An older dwelling might not have one though

Took mine off . Now its HOT water .
Bernie .

Busman I think has hit the nail on the head. I would try that. I bleed ours every 3 months to get the air out and water in. Other than that give the brand manufacturer a ring and pose the problem to them. How old is the unit.? Solar is ok if you intend remaining in the house long term but it is expensive.

I think the house sitters have been using some water for washing clothes etc so I'd give the thermostat a tweak & see if it's any different.
Electric one dot?

Thanks guys, G is going to do the valves right now and shall do the thermostat in the morning and see how we go from there. Yes the unit is electric and we had the ?element replaced a few yrs ago. It is the original heater from when we built in 1997 so I guess it has done ok

17 yrs out of a hot water cyl, must be a stainless cyl. Maybe we can set up a solar/electric hybrid system like we have here so the solar does most of the work and the electric becomes the back up.