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Old 13th January 2022, 23:11   #1
macafee2
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Default Chinese puzzle, one for the plumbers

A bit of back ground. Apparently this other "hot water" is used when the central heating water, has been heated to such a high temperature by the log burner, instead of it going back to the log burner it is used to heat water in a storage tank and this newly heated water is fed into the central heating when the log burner cools.

Normally a hot water tank has a coil in it for the heated water to go around and in turn heat the water stored in the tank. You then have a feed to the tank and a feed from the tank. This requires 4 pipes, feed to, feed from and 2 for the coil.

Here is the Chinese puzzle.
This tank only has 3 pipes.

Possibilities:-

1. I have had a mans look (not looked properly) and the 4th pipe is there.
2. There is no 4th pipe and we have been lied to.
3. Other, what ever that is.

I have emailed the manufacturer asking for a diagram to tell me what each point that seems to be for a pipe connection is for and to ask if 4 pipes is the minimum that should be connected.

In the mean time, I'm open to suggestions.

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Old 13th January 2022, 23:41   #2
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Generally on an indirect cylinder you will as you say have a coil where the inlet and outlet are in line above and below each other. Then you will have an inlet into the cylinder usually low level at the back of the cylinder. The hot water outlet of the cylinder is at the very top of it, again usually with an open vented cylinder combined with a vent to the header tank
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Old 14th January 2022, 09:08   #3
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Originally Posted by stocktake View Post
Generally on an indirect cylinder you will as you say have a coil where the inlet and outlet are in line above and below each other. Then you will have an inlet into the cylinder usually low level at the back of the cylinder. The hot water outlet of the cylinder is at the very top of it, again usually with an open vented cylinder combined with a vent to the header tank
Thank you. All seems to be as you say except for the inlet. I cant find it.


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Old 14th January 2022, 09:18   #4
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If the water is coming out of the hot taps then it must be going in to the cylinder. they are usually the opposite side of the heating coil, low down near the bottom Have fun Ian
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Old 14th January 2022, 11:29   #5
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If the water is coming out of the hot taps then it must be going in to the cylinder. they are usually the opposite side of the heating coil, low down near the bottom Have fun Ian
This is an "overflow" tank. The heated water does not go to taps but to the central heating and I think the coil in the hot water cylinder that serves the taps. We have a 290L tank for hot water to taps and a 490L tank that is an overflow of hot water. I cannot see us ever heating this 490L particularly if there is no feed to it

It is a complicated, poorly installed and poorly designed system. We intend to remove the tank that has 3 pipes to it, even if a 4th is found we will remove the tank, pump and motorised valves.
I will post an update once the manufacturer responds.
Oh buyer beware!

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Old 14th January 2022, 14:34   #6
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Ah, you may find it is not an indirect cylinder then. the purpose of the indirect cylinder is to pass the heat from the central heating water to the domestic hot water without contaminating it.
It could well be that it is a direct cylinder that doesn't actually have a coil fitted in it just two connections to allow the water to circulate. sounds a real Heath Robinson affair.
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Old 14th January 2022, 15:34   #7
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Ah, you may find it is not an indirect cylinder then. the purpose of the indirect cylinder is to pass the heat from the central heating water to the domestic hot water without contaminating it.
It could well be that it is a direct cylinder that doesn't actually have a coil fitted in it just two connections to allow the water to circulate. sounds a real Heath Robinson affair.
Heath Robinson, its worse than that Jim, that Jim, its worse then that Jim that Jim worse.

How on earth can someone forget to connect a feed?

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Old 14th January 2022, 17:29   #8
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Are you sure that the 3 pipes on the tank aren't in, out and vent? And that it's actually an expansion tank for the closed circuit heating system to heat the hot water in the 'normal' hot water tank? Not sure how that would be cross connected with the gas ch closed circuit but I guess it's possible with temp sensors and servo operated valves. But importantly, if I'm right, it's there for a very good reason. That reason could be to prevent terminal pressure build up (prevent a steam explosion). The log burner cannot be simply turned off when the hot water system is at max temp like the gas boiler can. In the old days of back boilers with open fires the heat from the fire could be directed to effectively control how much heating went into the system. This isn't going to be likely with a coil from a log burner.
I'd definately suggest consulting an expert on log burner integrations with c.h systems before even thinking of removing the large tank. You need to be absolutely clear of it's purpose before you can judge if it's necessary or not.
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Old 14th January 2022, 18:23   #9
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Where is the feed from the log burner to the tank? is it around the flue or fed through the fire? How is the tank venting off the pressure? Heating water through a log burner leads to uncontrolled temps unless there's some kind of thermostatic shut off. A gas boiler has many controls to stop overheated water but you might not have these kind of controls in that system. Like Dave says, it sounds a bit dodgy in how it's fitted.
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Old 14th January 2022, 19:52   #10
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Quote:
Originally Posted by Avulon View Post
Are you sure that the 3 pipes on the tank aren't in, out and vent? And that it's actually an expansion tank for the closed circuit heating system to heat the hot water in the 'normal' hot water tank? Not sure how that would be cross connected with the gas ch closed circuit but I guess it's possible with temp sensors and servo operated valves. But importantly, if I'm right, it's there for a very good reason. That reason could be to prevent terminal pressure build up (prevent a steam explosion). The log burner cannot be simply turned off when the hot water system is at max temp like the gas boiler can. In the old days of back boilers with open fires the heat from the fire could be directed to effectively control how much heating went into the system. This isn't going to be likely with a coil from a log burner.
I'd definately suggest consulting an expert on log burner integrations with c.h systems before even thinking of removing the large tank. You need to be absolutely clear of it's purpose before you can judge if it's necessary or not.
What you say makes sense but this tank is 490/495 litres. This seems awfully large. There are only 5 radiators and one of those is turned off but there is also underfloor heating that we have not used. Still 490/5L is still very big. All 3 pipes have motorized valves fitted and I would have thought only the flow in or flow out would need a valve to control flow through the coil. Why would the vent need one? The vent connects to the central heating I think. There is an expansion vessel connected to the central heating return but that is in another room. I would need to double check but in the loft either the flow or return to the log burner has a pipe that goes to a header tank, would this not double as expansion. I am sure the other pipe has a pipe connected but I cant think where it goes. This flow and return for the log burner go through a coil in the loft cylinder, the heated water goes to the central heating. There are 2 thermostats connected to the central heating flow at the top of this water cylinder. The first is set to about 30 degrees, when at 30 degrees it opens a valve or two or 3 goodness knows and may or may not start a pump and heated water is then sent to the central heating. The second thermostat is set to about 80 degrees, when this gets to temperature heated water is sent to the 490/495 water cylinder and opens a motorized valve to allow flow into the 490/5 cylinder, I don't know about pumps or any other motorised valves opening.

Avulon, does any of the above make sense? You have had a very good thought, thank you for piping up, any more thoughts?

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