No hot water: Unvented Santon Boiler

16 Mar 2022
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United Kingdom
Hi Guys,

Recently I noticed my hot water running slightly mild in temps and then eventually cold. I have a Santon Premier Plus Unvented hot water system, which has a top booster and a bottom part. For normal use over the last 5 years I've been using the lower larger part of the tank on a timer to come on twice a day.

I've just tried the upper part booster part of the tank and it seems to work in heating the water.

I'd be grateful if you have any ideas on what might be up with the lower part? A neighbour suggested that it might be the thermostat / limescale.



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As it's what called a direct system then it has 2 immersion elements - one in the top 1/3 as a booster for smaller amounts of HW usually on a boost times switch and the lower main immersion element to heat the whole cylinder on a timer as you suggest.

If the lower immersion heater is no longer heating the cylinder then it can really be only one of 2 things. The timer has failed and no longer supplies power to the immersion element or the element/stat itself has failed and needs to be replaced. Both would need an electrician and/or a plumber to ascertain and repair.
Last edited:
On our unvented cylinder the thermostat had failed. It unplugged from the end of the immersion heater and was easy to change, but ours doesn’t look like yours. Maybe removing the cover would help

As Madrab says above, an electrician could figure it out


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