solid fuel heating

nadiahealy

could somebody tell me why stove does not do the gravity circuit,stat is located on flow pipe as it comes of the stove,pipe then rises up the wall rising all the way across to hotpress,drops down to flow on a twin coil cylinder and return continues on down under floor and back to return on stove to make the loop,why is the hot water not pushing itself round without aid of pump

aujopimur

Is the return connection on the cylinder higher than the flow connection on the stove, i.e. is the cylinder raised, if not it needs to be.

nadiahealy

yea its slightly lower than flow on stove,i take it thats where the prob is.

Curly Judge

If the flow pipe is of an adequate size, [minimum 3/4 inch, depending on boiler output]
And if the flow pipe is rising continually to where it enters the top of the cylinder coil, it should work.
The return pipe should fall directly back to the boiler. It's okay for it to drop down to floor level and run horizontally before turning up to the boiler return tapping.
Check that the flow pipe is vented at the highest possible point.

nadiahealy

yea will check the vent pipe,i measured height of return on cylinder its bout 5 inches lower than flow on stove do u think thats the prob, i will raise it higher but wont be an easy task,would hate for it not to work after that hastle

shane0007

nadiahealy wrote: »

could somebody tell me why stove does not do the gravity circuit,stat is located on flow pipe as it comes of the stove,pipe then rises up the wall rising all the way across to hotpress,drops down to flow on a twin coil cylinder and return continues on down under floor and back to return on stove to make the loop,why is the hot water not pushing itself round without aid of pump

I think the key here is "drops down to flow on a twin coil cylinder...". Natural gravity will only work on a continuous rise to the coil where the heated water fromthe stove is less dense and will naturally want to rise to the coil where the coil will cool the water temperature flowing through it by transferring that heat into the water within the cylinder, thus making is more dense and causing it to naturally fall.
It will travel along the pipe until it meets the elbow that drops the pipe down to the cylinder. Here you have less dense water wanting to rise with more dense water below it. If the pump does not kick in, it will not pull the heat down and you will probably experience some pipe banging until this occurs. The downside is if you lower the temperature on the pipe stat to say 40C to bring it on earlier, then the pump will not turn off until the temperature falls below 40C. This means that once the fire in the stove goes out, pump will use the heated cylinder as the heat source and cool the cylinder temperature to 40C using the stove as the heat dump.

The pipe run should also always be in 1" copper at all times (flow & return) with no restrictions, i.e. pumps, valves, non-return valves, etc. The run should be no more than approx 7.5m (25f) in length subtracting 0.5m for each 90 elbow or 0.3m for every sweeping bend (formed with pipe bender).

Gravity circuits are VERY slow moving so they need every encouragement to circulate. Any restrictions will hamper this.

The circulating pump should also be on return from the rads back to the stove so that it pulls both from the rads and the also from the return in the cylinder. If it is on the flow it can cause the most of the heat to go to the rads and very little to the cylinder, rather than heat to both.

nadiahealy

my cylinder return is lower than stove flow,i was told it needs to be higher in order for it to work,i think thats the prob

omah27

Hi i have same problem with my stove, just wandering did u rise tank
to fix it ?

nadiahealy

Yea i rise the cylinder allowing the return of the coil to be 4 inches higher than the flow on the stove and gravity circulation worked a treat

freddyuk

nadiahealy wrote: »

Yea i rise the cylinder allowing the return of the coil to be 4 inches higher than the flow on the stove and gravity circulation worked a treat

It is very useful and polite to offer feedback if a thread has solved your problem. There is nothing more annoying than finding a thread with exactly your problem and finding it leads to a dead end with no answer.

omah27

Dat is great news,the return is 4 inches lower then stove flow so i
will rise my tank during the week and let u know how i get on.
Thanks again.

nadiahealy

you would also need to make sure the flow pipe is rising all the way to cylinder from stove,no dips and no restrictions,no pump or non return valve on pipe run on the flow or return as this would also prevent gravity circulation.best of luck;)