There may be isolating valves on the secondary pump, post a photo,
Boiler firing constantly for hot watere
- Thread starter pwater
- Start date
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Hi, thanks yea there are, have now closed them and will see if that reduces the hourly calls for heat!
So this didn’t make any difference. So I am not going down a rabbit hole, the tank when isolated holds temp without firing the boiler for 6/7 hrs. So should I expect at least 3/4hrs when the tank isn’t isolated, but all hot water circuits are closed?
If so it would indicate something is slowly leaking a bit of hot water, so then I can concentrate on that!
Thanks
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By isolated, do you mean you've turned off some sort of valve which has stopped any of the hot water leaving the cylinder and going to the taps? What do you mean by all hot water circuits are closed?
Hi, yep, I turned off the valve on the flow after the cylinder so no water could leave it, this way the tank kept temp and didnt call for heat over a 6/7hr period. Soon as I opened it again, it was back to normal, every hour or so.
When it calls overnight, all the taps/showers etc are off, and nothing is on that would draw hot water, if that makes sense!
Ta
Paul
That makes sense. I'm not totally clear what you mean by the following, though
What is the 3/4hrs? I thought the boiler was firing every hour or so. Did you mean 45 minutes when you wrote 3/4hrs, or about 3 or 4 hours?
So currently it fires every hour to top itself up, however when it was isolated it didnt call once over a 6/7hr period, so I know the tank xcan hold the heat. So I am just trying to understand if when the tank isnt isolated (i.e flow is open, but no taps/showers on) I cshould expect it to hold heat for longer than 1hr, ie. I would expect it could hold the temp for a few hours so long as there is no usage?
Ta
Paul
I see what you are asking. I am sure most modern cylinders go several hours without calling for more heat if no hot water is used. I believe they normally have to drop at least ten degrees before asking for heat again. It's not something many people get to test in practice, because usually the hot water runs on a timer rather than being left on constantly. I have occasionally left my hot water programmer in the on position for several hours after the cylinder has been heated and the cylinder has never dropped low enough to call for heat again.
https://mcdonaldwaterstorage.com/hot-water-cylinder-recovery-times/#:~:text=When the cylinder is up,reheat time will be affected.
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thanks! I spoke to santon/back who said that as soon as the tank drops 1 degree it will call for heat, which isn’t ideal, but I still must be losing water somewhere to cause it to drop….the mystery continues!
My plumber has said we can put a flow meter on the hot water, see if we are losing any when no outlets are open, so will see what that turns up!
With stratification, I could see the sensor at the bottom of the tank registering a 1 degree fall quite soon after the cylinder has reheated.
I can't see any cylinder stat having a switching hysteresis of 1 degree, I'd say 8C to 10C normally and a minimum of 5C to 6C, I wonder it if it could be just the boiler firing on/off on its own stat if the motorised valve end switch is defective?, if you left both CH & HW programmed off then it may show up something because the boiler should not fire then even if all the HW drained off during the night.
Yea, it does seem a bit OTT but can only go on what they have said, if it is larger then it’s a bit more worrying as I would need to be losing a decent bit of water every hour to cause the temp to drop that much. I have verified the tank seems ok and will hold the heat ok.
My flow temp at the top of the tank only varies by 2/3 degrees all day, maybe shows a 1-1.5 degree drop before the tank fires again…
It’s definately the tank firing the boiler, the pump and zone valve are switched by it and they both come on. The pump is pretty recent and the zone valve is only a few weeks old, I just can’t see where I would be losing enough water constantly to cause it to fall in temp so fast, only place is really under the ground floor somewhere…
Thanks for all your inputs
The cylinder thermostat is at the bottom of the tank. That area naturally cools more quickly by stratification. I think it could easily lose 1 degree in an hour and trigger the boiler to come on. There might not be a leak at all. Why don't you have a timer/programmer for the cylinder? I would have thought that was unusual
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