Boiler still heating water despite immersion having recently heated the water
- Thread starter UKMO
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You have set the cylinder stat for the boiler. Turn off electric supply for immersion, remove white cap and adjust temperature dial
Just want to see if a burner flame signal comes on, no need for above, but may have to run off 10 litres of HW or so to make cylinder stat close and fire the boiler, there is a burner ON symbol displayed, D, below.
Thanks danfre. I have removed the cap and I can’t see a temperature dial. There is one red thing which looks adjustable but doesn’t have any indications of temperature units on it?
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Thankyou. I did this and it worked as it seemingly should do. I turned the dial up to maximum and the boiler immediately fired up and then when I turned it back down to 50 it turned off. So that seems to be working fine. I’m now trying to adjust the immersion thermostat but struggling to see how to do that. When I removed the white plastic cap it wasn’t obvious how to adjust the immersion temperature. There’s a red dial but has no indicators of temperature on. It’s currently on the maximum but I don’t know what that is in temperature
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Why are you turning down the immersion stat?, you are trying to figure out why the immersion apparently isn't getting the cylinder up to temperature?.
Also remember the cylinder is supposed to be heated to 60C at least once per week to avoid the risk of legionella.
Also remember the cylinder is supposed to be heated to 60C at least once per week to avoid the risk of legionella.
One of the other posts above suggested checking the immersion stat (which seems sensible) so I have done and can't be sure of what temp is set to as it doesn't have any temperature scale/numbers on it. However, as it seems to be set to the maximum then I take your point about minimising the legionella risk and keep that at the maximum. Now that i have done as suggested i am going to do another test tomorrow when the immersion has been on all night and set the boiler timer to come on in the morning to heat the water and see if it does or not. I would not expect it to and now having done the test you suggested by testing the boiler stat on the cylinder i'm more confident it is all doing what it should. The big test will be at night to see if the water is still hot and if the volume of hot water is as expected. I'll report back.
For now, i can't thank you and everyone enough for the input. This is my first visit to this forum and i am very impressed and grateful by the generosity of the time and knowledge provided.
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the boiler has absolutely no clue what temperature the HW is in the Cylinder, it gets an on/off signal from the cylinder thermostat, if the cylinder thermostat is satisfied the boiler wont fire, if the cylinder thermostat is calling for heat then the boiler will fire
That will maximise the scalding risk
Legionella does not multiply above 45C
Above 50C it will be killed. If your water is stored at this temperature for an hour and a half, it will all be dead. Hotter kills it quicker. The water at the top of the cylinder (about to be used) will be the hottest. If your stat is at the bottom of the cylinder (coolest part) 50C or even 45C will be plenty. The water from the taps will be hotter.
As you have an unvented cylinder it is not likely that any will get in and survive.
So, let's simplify this...
Heated by gas boiler gives you a full cylinder of hot water?
Heated by immersion you only get a partial cylinder of hot water?
Would the above be correct?
Heated by gas boiler gives you a full cylinder of hot water?
Heated by immersion you only get a partial cylinder of hot water?
Would the above be correct?
Not quite.
I get a full tank of hot water by either immersion or gas boiler. But what seems strange is that even after heating the tank by immersion, the gas boiler would still come on via timer and heat the water.
However, from following above advice it seems to have worked. After adjusting the stat on the cyclinder, yesterday I put the immersion on at lunchtime. Boiler did come on briefly (via timer) a couple of hours later but only for a short while. Water stayed hot all day and evening. So all seems to be as normal. I will be testing it again today
Thanks again for all the input. Very much appreciated and saved me an expensive plumber visit
So, for the boiler to fire and heat the cylinder, the temperature in the cylinder, as detected by the cylinder stat, would have had to drop enough, since the last period of heating, via the immersion, to initiate a demand.
Yes, but due to the very low location of the cylinder stat, using 10/15L of HW will cause the boiler to fire but it should on;ly have to reheat this volume of water as the water above it should be hot.
Thanks for all the help. Everything is working as it should now. The immersion is coming on at night and when I have surplus solar power. This usually means the water is hot and the boiler doesn’t need to come on or, if it does, it’s only for a short while to give the water temp a boost. I am very grateful for everyone’s assistance. Thankyou
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