S
SmashyD
hi louis
Sorry, only just received notification of your post.
Problem i can see with a check valve is reduced performance in the gravity circuit but i'm not sure about that.
I would say your cylinder is fine at that position. My heat leak rad may be a long way away but much of that is distance is in 28mm and only reduces to 22mm for the last 2 or 3m. Also to be honest i'm not sure it is that good really as i lose some heat in the loft. ( It is fitted as a safety device rather than an effective radiator.
Building regs state that the heat leak pipe work should be 22m and reduce to 15 only for the last 300mm maximum. This is important for gravity circulation. It is a very weak motive force and any friction introduced can slow it down so much that you will lose as much heat from the pipework as you are trying to convey to the cylinder! this can bring the heat conveyance to a halt. Until i insulated everything really carefully my system wasn't very effective at all. If you do fit the heat leak a distance away you have to remember that all your fittings (including straight unions) have a significant effect on the flow resistance so you will need to bend the pipe rather than use elbows, etc. (do not use plastic anywhere on the gravity side).
I'm a bit puzzled as to why you're getting reverse circulation to the point where your cylinder is cooling right down - just goes to show how effective gravity can be for transfering heat!
Also dont rely on the foam that the cylinder comes with, it will lose a significant amount of heat over the course of the night. The cylinder i have is foam covered but without a jacket loses 2.7kw/h!(written on the label) Put a jacket over it as well. Try double insulating the 28mm pipe work in the loft, cover it over with loft insualtion aswell and insulate all the way to the stove - you will lose a lot of heat through the pipes where they come down from the ceiling to the stove . I think the pipework heatloss may be where your problem lies.
At the end of the day gravity works simply because cold water is heavier than hot water. Therefore once you have cold at the bottom and hot water at the top of the circuit it should want to stay there providing there is no great change in the temperature of the stored water.
Let us know how you get on. I take it you have already fitted that flap valve - how is that working out?
Regs SmashyD
Just been thinking about the way your plumbing is set up.
You say that you have 4 tappings on the boiler - 2 for gravity and 2 for radiators and you have a long gravity circuit.
Have you considered piping it a different way.
Another way in your situation may be incorporating an injector T as in the second diagram (fig 6) in the manual. This has the effect asssisting the gravity circuit when the pump runs therefore heating your cylinder much more effectively. C/H often steals all the heat from the circuit when the pump runs.
Use thermostatic rad valves (all bar one) and once the house is warm, if the stove is still hot the pump will run the gravity circuit pretty exclusively. Wire in a high limit pipe stat on the cylinder flow from the boiler and it acts as a safety cool down for the stove by getting rid of excess heat round the rad circuit. Obvously only when there is power - it doesn't replace a heat leak rad.
Once you've got your heat up there your half way there.
BTW: A few questions:
Could the pump be running after the boiler has cooled to below that of the cylinder? Not sure how this might effect it but it might cause some movement. The pump should be wired to stop if the return or flow temp is too low.
How long does it take for the boiler to heat the cylinder to 60c?
Are you reaching 60c, or higher - too high?
Do you have a thermometer for checking pipe work, boiler and cylinder? (if not, consider getting one - it's like a sixth sense where plumbing is concerned)
Is there any kind of temperature control for the water?
What controls do you have other than the stove thermostat control?
Does the stove ever kettle or boil?
Is your f&e tank (or for that matter, the cold water storage tank) getting hot? BTW: Does it conform to the latest building regs for solid fuel systems? (it has to be able to handle 110c including ball valve and overflow: BS4213). Check the "HSE safety alert on scalding risk from domestic hot water systems"
regs
Sorry, only just received notification of your post.
Problem i can see with a check valve is reduced performance in the gravity circuit but i'm not sure about that.
I would say your cylinder is fine at that position. My heat leak rad may be a long way away but much of that is distance is in 28mm and only reduces to 22mm for the last 2 or 3m. Also to be honest i'm not sure it is that good really as i lose some heat in the loft. ( It is fitted as a safety device rather than an effective radiator.
Building regs state that the heat leak pipe work should be 22m and reduce to 15 only for the last 300mm maximum. This is important for gravity circulation. It is a very weak motive force and any friction introduced can slow it down so much that you will lose as much heat from the pipework as you are trying to convey to the cylinder! this can bring the heat conveyance to a halt. Until i insulated everything really carefully my system wasn't very effective at all. If you do fit the heat leak a distance away you have to remember that all your fittings (including straight unions) have a significant effect on the flow resistance so you will need to bend the pipe rather than use elbows, etc. (do not use plastic anywhere on the gravity side).
I'm a bit puzzled as to why you're getting reverse circulation to the point where your cylinder is cooling right down - just goes to show how effective gravity can be for transfering heat!
Also dont rely on the foam that the cylinder comes with, it will lose a significant amount of heat over the course of the night. The cylinder i have is foam covered but without a jacket loses 2.7kw/h!(written on the label) Put a jacket over it as well. Try double insulating the 28mm pipe work in the loft, cover it over with loft insualtion aswell and insulate all the way to the stove - you will lose a lot of heat through the pipes where they come down from the ceiling to the stove . I think the pipework heatloss may be where your problem lies.
At the end of the day gravity works simply because cold water is heavier than hot water. Therefore once you have cold at the bottom and hot water at the top of the circuit it should want to stay there providing there is no great change in the temperature of the stored water.
Let us know how you get on. I take it you have already fitted that flap valve - how is that working out?
Regs SmashyD
Just been thinking about the way your plumbing is set up.
You say that you have 4 tappings on the boiler - 2 for gravity and 2 for radiators and you have a long gravity circuit.
Have you considered piping it a different way.
Another way in your situation may be incorporating an injector T as in the second diagram (fig 6) in the manual. This has the effect asssisting the gravity circuit when the pump runs therefore heating your cylinder much more effectively. C/H often steals all the heat from the circuit when the pump runs.
Use thermostatic rad valves (all bar one) and once the house is warm, if the stove is still hot the pump will run the gravity circuit pretty exclusively. Wire in a high limit pipe stat on the cylinder flow from the boiler and it acts as a safety cool down for the stove by getting rid of excess heat round the rad circuit. Obvously only when there is power - it doesn't replace a heat leak rad.
Once you've got your heat up there your half way there.
BTW: A few questions:
Could the pump be running after the boiler has cooled to below that of the cylinder? Not sure how this might effect it but it might cause some movement. The pump should be wired to stop if the return or flow temp is too low.
How long does it take for the boiler to heat the cylinder to 60c?
Are you reaching 60c, or higher - too high?
Do you have a thermometer for checking pipe work, boiler and cylinder? (if not, consider getting one - it's like a sixth sense where plumbing is concerned)
Is there any kind of temperature control for the water?
What controls do you have other than the stove thermostat control?
Does the stove ever kettle or boil?
Is your f&e tank (or for that matter, the cold water storage tank) getting hot? BTW: Does it conform to the latest building regs for solid fuel systems? (it has to be able to handle 110c including ball valve and overflow: BS4213). Check the "HSE safety alert on scalding risk from domestic hot water systems"
regs
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