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After getting a solar diverted I noticed not an awful lot of energy going into the immersion heater, even when we’ve had showers in the morning (and has heating is switched off). There’s a thermostat on the tank and it’s set pretty low, how do I tell if that’s just for the immersion or also for the gas?

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The thermostat is sensing the temp of the water at what ever point the sensor is in the tank - end of. The thermostat could be used to switch on the gas but more likely it controls the immersion heater and you have another one for the gas. If you follow the cable from the thermostat does it go to the immersion.

Remembering the diverter is only diverting excess power not used in the house then at this time of the year this amount can be very small compared to your needs and indeed somedays there is none. At this time of the yr i have my thermostat set very high on max so as not to restrict the good days and help with the poor days. In summer i turn it down to a min.

How effective the diverter is at this time of theyear depends a little on where the immersion is fitted, water usage and heat loss in tank and pipes.
 

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I believe that you need to find both thermostats and set the immersion one to a slightly higher temperature than the gas one. Then you programme your gas system to heat only in the evening i.e. after the solar has done it's stuff. If there has been a lot of solar that day, the gas system just won't run . If there has been very little, it will top it up to a tankful.

This works well for us but we are only a couple and have a huge tank. You'd need to think it through for a family.
 

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The thermostat is sensing the temp of the water at what ever point the sensor is in the tank - end of. The thermostat could be used to switch on the gas but more likely it controls the immersion heater and you have another one for the gas. If you follow the cable from the thermostat does it go to the immersion.

Remembering the diverter is only diverting excess power not used in the house then at this time of the year this amount can be very small compared to your needs and indeed somedays there is none. At this time of the yr i have my thermostat set very high on max so as not to restrict the good days and help with the poor days. In summer i turn it down to a min.

How effective the diverter is at this time of theyear depends a little on where the immersion is fitted, water usage and heat loss in tank and pipes.
Thanks Ken,
Generation should be ok, 35kwh yesterday from our 8kw array.

I'll have a good look and see if there's a second thermostat, but I could only see the one with a cursory glance (shelves in the way make getting to the cylinder a bit of a faff).
 

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I believe that you need to find both thermostats and set the immersion one to a slightly higher temperature than the gas one. Then you programme your gas system to heat only in the evening i.e. after the solar has done it's stuff. If there has been a lot of solar that day, the gas system just won't run . If there has been very little, it will top it up to a tankful.

This works well for us but we are only a couple and have a huge tank. You'd need to think it through for a family.
Thanks Tom, setting the gas on evening only is a good idea. Not sure it will work too well for us though as the kids have a bath every other night and then we have showers in the morning, so I'd be worried about not having enough for a shower without a morning topoff, but there again maybe I can program it to just run for a very short period - i'll have to have a look!
 

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I think your immersion heater thermostat is under the black cover at the bottom of the photo. The temperature scale is on it.
 

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Yeah it seems the one thermostat is used for both the immersion heater and the gas boiler input so I can't set them differently. It was set on what looked like 37C so i've tweaked it up to 65C and switched the gas heating to only come on once in the early evening after sunset. about 5kwh got diverted today after one bath last night and one shower this morning before, the Eddi reported max temp reached so that seems to have done the trick.
 

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I'd start by turning the immersion off, and the gas thermostat down. Then turn on the gas h/w heating and progressively turn up the gas thermostat until you get a tank of h/w which is the minimum temperature that you can work with.

I keep the gas heating turned off until 1st thing in the morning and just use it to top up whatever the immersion has managed the day before to the minimum I can cope with.
 

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I had Evohome installed in my previous home. Hot water was stored in an unvented cylinder. The cylinder had a single normal thermostat for both gas and electric re-heating - with a TopStat to cover thermostat failure. When I had the Evohome Hot Water kit installed, my G3 engineer said that it was safety critical that the kit thermostat was wired in series with the existing thermostats with the normal thermostat set to a slightly higher than the kit set temperature.
 

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Electrical immersion heaters normally have a thermostat switch directly built into the heating element itself with the dial for this under a round cover.
 

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Not sure it will work too well for us though as the kids have a bath every other night and then we have showers in the morning
Provided the gas boiler stop heating the water before your morning shower, the showers will leave "space" to store the heat from PV.
 

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Electrical immersion heaters normally have a thermostat switch directly built into the heating element itself with the dial for this under a round cover.
Also, if you look at Edd's photo, the cable going to the immersion heater is thicker than that going to the separate thermostat, so I would also expect the immersion heater thermostat to be under the black cover, and the separate thermostat to be for the gas.
 

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Thanks again for all the replies, I’ve had another poke about today and there is indeed a separate stat under the black cover. So I now have the immersion on about 65 and the gas on 40. Hopefully that’ll all work out ok, just have to remember the kitchen tap will be HOT on a sunny day!
 
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