OK, if the boiler fires every say 25 minutes with a 1.5C drop in temp then its easy enough to work out the loss. Dont know what size cylinder but assuming 200L then loss/hour is 200*1.5/860*60/25, 0.837kwh or 0.837*24, 20kwh/day, unbelievable almost except its a leak as you suspected.
Boiler firing constantly for hot watere
- Thread starter pwater
- Start date
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Good question, the setup came with the house, so I have just been trying to understand it all and I think that’s the next logical step! The part I don’t understand however is if I isolate the tank, it doesn’t lose anything and the stat doesn’t fire the boiler, so I must be seeing some water leaving the tank for the cold to flow in and cause that..?
I’ve turned the power to the tank off tonight, will see what the temp is like in the morning.
Thanks
Wouldn't stratification actually tend to keep the bottom hotter assuming no leaks as the water in the top will cool faster, also the layer of hot water above the cold should tend to heat the bottom by conduction, thats what happens to mine at any rate.
Yea so it’s firing every 60/90 mins it seems, mostly every 60 mins almost right on the nose. It’s a 300L tank, so that would be even higher then?
Is there any way to equate that to how much water I would be “losing” to cause that?
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That seems to make sense. I'd forgotten about that!
A 300L cylinder loosing 1.5C/hour is a loss of 0.523kwh/hr or 12.6kwh/24hrs, you are definitely leaking water IMO.
Quite difficult, but what you might do is........
open a hot tap to give a fairly low flowrate of ~ 3LPM or so and have a big bucket & stopwatch to hand, as soon as the boiler fires up, shut the HW tap.
Put your bucket under the hot tap and just when the boiler stops firing, open the HW tap (to give that ~ 3LPM) into the bucket and start the stopwatch at exactly the same time, as soon as the boiler refires, stop the stopwatch and shut the HW tap, measure this, you know the time it took and this will give you the leakage rate. QED
You probably don't even need to time it but no harm because once you measure the volume of water then you know its loosing this volume in 60 minutes or whatever the interval is between the firings, if this volume is say 10 litres then the leakage rate is 10/60, 0.17LPM.
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So I left the power to the tank off all night, around 8 hours. I moved the thermostat to see where it clicked before I turned it back on, still seemed to be sitting around 4, so it didn’t think it had lost 10 degrees or anything. When I turned it on, it only called for hot water for 15mins (I.e the same time I am seeing when it calls every hour)…so it can’t have lost much.
I am now thinking it’s not losing any water, or really much heat, and this may be more a design issue. The boiler flow to the cylinder and the return run from the tank on the first floor down to the garage, no idea what route the pipe takes, but the zone valve which closes off this circuit is by the boiler. So I am wondering, due to where the thermostat seems to be near the coil, does this pipe work basically act like a massive coil and cool the water in the coil, causing that small drop which seems to kick the thermostat off.
I have attached a probe to each side of this pipe on the cylinder, will see if I can find any pattern in the temp of those pipes and it firing.
My initial thought is it needs to have this pipe closed closer to the cylinder, so a zone valve on the boiler flow just before it goes into the cylinder. Fingers crossed
Thanks!
I am now thinking it’s not losing any water, or really much heat, and this may be more a design issue. The boiler flow to the cylinder and the return run from the tank on the first floor down to the garage, no idea what route the pipe takes, but the zone valve which closes off this circuit is by the boiler. So I am wondering, due to where the thermostat seems to be near the coil, does this pipe work basically act like a massive coil and cool the water in the coil, causing that small drop which seems to kick the thermostat off.
I have attached a probe to each side of this pipe on the cylinder, will see if I can find any pattern in the temp of those pipes and it firing.
My initial thought is it needs to have this pipe closed closer to the cylinder, so a zone valve on the boiler flow just before it goes into the cylinder. Fingers crossed
Thanks!
Surely the boiler isnt firing for 15 minutes every hour?, if so, even if the cylinder coil is only emitting say 8kw then you are loosing 2kwh/hr or 16kwh over a 8 hour period. Maybe tonight, before retiring, let everything enabled and all valves opened and take a photo of the gas meter, in the morning, before any HW drawoff, take another photo.
Also if this apparently tiny 1.5C or so stat hysteresis is true then the tiniest movement of the setting dial should trigger it, next time it cuts out then if you increase the setting until the boiler refires then you will get a good feel for the "real" hysteresis.
Overall the gas meter monitoring overnight will be the most revealing IMO.
Also if this apparently tiny 1.5C or so stat hysteresis is true then the tiniest movement of the setting dial should trigger it, next time it cuts out then if you increase the setting until the boiler refires then you will get a good feel for the "real" hysteresis.
Overall the gas meter monitoring overnight will be the most revealing IMO.
Hi
Yep it’s pretty much every hour. I did record the gas meter after you mentioned it before, problem is the CH comes on around 5am so I am not able to check it before that so I get the CH mixed in as well.
It takes around 10 mins for the boiler to come up to temp from pretty much cold, then I assume just a few mins to bring the tank up it’s tiny drop, as you can see in the attached.
I barely need to touch the stat setting for it to click and fire, it’s set to 4 which is around 60degrees, so it’s not centrally losing much if any heat.
In addition to the zone valve, I am also wondering if the stat is maybe just old, the tank itself is 20 years, so maybe wouldn’t be the worst thing to refresh it, especially if most stats would need a few degrees drop to fire.
Paul
Attachments
You should have another stat for the bottom immersion heating element, check if a tiny movement makes it click ON/OFF, if not and it takes more movement of the dial then the other stat requires renewing, its just not creditable that any mechanical cylinder stat will have a hysteresis of 1 to 1.5C.
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Do you have a graph for the flow temperature? The one you have posted says return, I think.
What is the boiler model and what is the output kW?
Are you 100% sure it is the cylinder which is firing the boiler, not the heating circuit?
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