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direct hot water combination ccylinder

View the thread, titled "direct hot water combination ccylinder" which is posted in Bathroom Advice on UK Plumbers Forums.

D

desrob

has anyone came across these cylinders the problem being there is no water in top part,cold feed tank?.but i can still draw water off, at both cold and hot water taps,it is an old model 15-20 yrs?, there is two tappings at two thirds up what go into a t.m.v and then on to a shower, the hot is t'd off this feeding all other hot out lets,and the cold is direct,there is what i presume is a vent going into top tank and a hole in the bottom (cold feed ?),the immersion heater has blown because i think the tank is empty were the immersion heater goes in ,if isolate the cold supply to cylinder i get no flow at taps straight away hot and cold but no water going into top tank,please help me out here ,if i could split cylinder in half i'd have a better understanding if any diagrams out there,remember old model
 
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They are designed in such a way that if cold fill is isolated the hot will stop running once cold water in top part is used. Leaving the cylinder full. However a tapping may have been added lower down the cylinder (perhaps to shower) (or wronge tapping used say flow)which would account for emptying. Might be just a worn out immersion heater.
 
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justlead1 said:
They are designed in such a way that if cold fill is isolated the hot will stop running once cold water in top part is used. Leaving the cylinder full. However a tapping may have been added lower down the cylinder (perhaps to shower) (or wronge tapping used say flow)which would account for emptying. Might be just a worn out immersion heater.
Click to expand...
immersion brand new,so what your saying if the cold feed to top tank is lets say blocked etc the cylinder will remain full and supply both hot and cold outlets at mains pressure as is happening
 
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justlead1 said:
No Sir. The cold to taps may well continue but the hot will stop if feed via the cylinder
Click to expand...

hot is feed by the cylinder ,this is the problem,it's still running at mains pressure even though the the cold feed tank at top of cylinder is empty as i have already said,i'm begining to think there might be an integral air bubble what as failed,this is why i could do with better understanding of the cylinder within,confusing to say the least going back on monday.
 
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It is not a direct combination cylinder, it is an original Gledhill Pulsacoil. The tank on top is fills the cylinder (thermal store). The hot water is supplied via a coil running through the thermal store. Early models had no ballcock fitted and the householder had to top them up manually (the water evaporated over time) which they rarely if ever did. If the store was becoming empty they would have noticed the hot water getting progressively cooler.
Drain the cylinder and fit a new immersion and fill it up again. If there is no ballcock on the tank fit one.


Here is a quick drawing of what it is, not totally accurate but near enough to give you the jist of it.
pulsacoil.JPG

Later versions had plate heat exchangers and pumps
 
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tamz said:
It is not a direct combination cylinder, it is an original Gledhill Pulsacoil. The tank on top is fills the cylinder (thermal store). The hot water is supplied via a coil running through the thermal store. Early models had no ballcock fitted and the householder had to top them up manually (the water evaporated over time) which they rarely if ever did. If the store was becoming empty they would have noticed the hot water getting progressively cooler.
Drain the cylinder and fit a new immersion and fill it up again. If there is no ballcock on the tank fit one.

that makes a bit of sense,your pic is similar to the set up i've encountered,the cold feed goes on to the top tank,when i draw hot water i get it at mains pressure or there abouts and the cylinder does not empty and refill as i expected,it goes through a, t .m.valve,but if it goes through a coil as you suggest i'll only get a coil full of hot water and then it will start to get cooler as the water is drawn through the coil,how are you meant to fill a bath etc
Here is a quick drawing of what it is, not totally accurate but near enough to give you the jist of it.
View attachment 2090

Later versions had plate heat exchangers and pumps
Click to expand...

tamz said:
It is not a direct combination cylinder, it is an original Gledhill Pulsacoil. The tank on top is fills the cylinder (thermal store). The hot water is supplied via a coil running through the thermal store. Early models had no ballcock fitted and the householder had to top them up manually (the water evaporated over time) which they rarely if ever did. If the store was becoming empty they would have noticed the hot water getting progressively cooler.
Drain the cylinder and fit a new immersion and fill it up again. If there is no ballcock on the tank fit one.

that makes a bit of sense,your pic is similar to the set up i've encountered,the cold feed goes on to the top tank,when i draw hot water i get it at mains pressure or there abouts and the cylinder does not empty and refill as i expected,it goes through a, t .m.valve,but if it goes through a coil as you suggest i'll only get a coil full of hot water and then it will start to get cooler as the water is drawn through the coil,how are you meant to fill a bath etc
Click to expand...
 
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the water you draw off goes through a coil and it is heated by the water in the cylinder as it passes through, the water in the cylinder never changes
 
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Look at the drawing.
As Mike said the water in the cylinder never changes. It just sits there and heats up usually to around 70 - 80º.
The mains water runs through the coil inside the cylinder and the heat is transferred from the surrounding water. When it comes out the other side it is 60º plus so it runs through a tmv and gets blended with cold to reduce the temperature to 55º. It will continue to run hot until the temperature of the heatstore has been depleted.
Look up thermal store.
 
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tamz said:
Look at the drawing.
As Mike said the water in the cylinder never changes. It just sits there and heats up usually to around 70 - 80º.
The mains water runs through the coil inside the cylinder and the heat is transferred from the surrounding water. When it comes out the other side it is 60º plus so it runs through a tmv and gets blended with cold to reduce the temperature to 55º. It will continue to run hot until the temperature of the heatstore has been depleted.
Look up thermal store.
Click to expand...

i understand the concept totally my point being the heat transfer been not very effective
 
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desrob said:
i understand the concept totally my point being the heat transfer been not very effective
Click to expand...
That is because it has been near empty. It takes a while to evaporate 150 litres of water.
They work fine if there is water in them and as said check for limescale in the coil.

The only things that can possibly go wrong with these are
Lack of water in cylinder
Immersion (see above)
Scaled coil (if in a hard water area)
TMV.
That is it
 
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tamz said:
That is because it has been near empty. It takes a while to evaporate 150 litres of water.
They work fine if there is water in them and as said check for limescale in the coil.

The only things that can possibly go wrong with these are
Lack of water in cylinder
Immersion (see above)
Scaled coil (if in a hard water area)
TMV.
That is it
Click to expand...

thankyou i appreciate the advice.
 
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had to fit a new immersion to one of these last year, card on the side insisted it was to be a 14"immersion with 11" stat (hard to find) set at 70c
 
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