Reverse Circulation with Stove

[Louis]

Hi folks
Great forum thanks

I put a stove in a while back, one that heats the water and rads.

The natural circulation is plumbed to heat the hot water cylinder. Unfortunately when the stove is left overnight and gets cold, reverse circulation starts in the system and by morning time most of the heat is gone from the hot water cylinder

Any thoughts on the best way to stop this reverse circulation??

Thanks in advance
Louis

 

[nick penfold]

hey Louis, there's a load of great time served guys on here who can help, Im only just starting to cover this subject at college so probably best that i don't advise.

it may be easier for the guys to advise if you can give some more details such as the following

Is it a pumped system?
Maybe an S plan or Y plan set up?
Installed a balancing valve?
Where is the pump in relation to the vent and cold feed pipe?

sorry i can't help anymore but im interested to hear what the big boys have to say for my own education )

goodluck

A basic drawing from you showing you're piping would also be handy.

 

[sonray ltd]

as said a basic drawing etc of your layout as reverse circulation can be caused many ways. but is useally only a simple error of pipework.

 

[tipper]

What you need is some form of non-reverse valve/clack valve to stop reverse flow as it cools down.

Go and talk to you plumbers merchant about a check valve.

 

[Louis]

Thanks for the replies guys

Ok, the stove has two inlets and two outlets.
One inlet and outlet is used for the pumped system to the rads.

The other inlet and outlet are used for the natural circulation and safety system. It comprises of a 1 inch pipe going up to the attic and down through the coil in the hot water cylinder and then straight back to the stove.
There is nothing really to stop the reverse circulation in this circuit, in my view, and this is where the problem is.

Nick, I take it your comments apply to a pumped system. Although this is also a pumped system the problem is with the natural circulation part of it which does not use the pump.

Sonray, thanks for that, I would hope that something simple could be incorporated to prevent it. Does the above description give you enough info?

Tipper, since this is the safety circuit, it is supposed to be uninturrupted with any valves etc.. At least this is my understanding, although a non-return valve would seem like the easy option, if it were safe practice.
Any thoughts?

Thanks so far, hope you have enough info above.

 

[sonray ltd]

louis i take it you have your vent pipe coming off this side ?
as you say a vent pipe must be clear off any etc plus a anti gravity valve won't open under gravity.

so what is happenening when the stove is turned off ?
cold water is going back up the return pipe.

 

[Louis]

Sonray
Yes, the vent comes off the highest point on the 1 inch pipe in the attic and goes to the expansion tank in the attic.

When the stove is turned off and cools down, the heat in the hot water cylinder then starts the reverse circulation in the coil, which circulates back through the stove and is cooled down overnight leaving a luke warm or cold hot water cylinder in the morning.

The same thing actually happens if the hot water cylinder is heated with the electric immersion heater - after a while the stove water jacket will get warm because of the reverse circulation caused by this also.

 

[sonray ltd]

the feed/return is on the right way on the stove & cylinder?

 

[Mike Jackson]

I think the problem is the pipe running up into the attic and back down again. Once the stove and pipework have cooled down the cylinder is the hottest part of the circuit. Natural convection will cause heat to rise back up the pipe and start the reverse circulation. Other than the vent the coil needs to be the highest part of the circuit to stop this happening.

Mike

 

[tipper]

Tipper, since this is the safety circuit, it is supposed to be uninturrupted with any valves etc.. At least this is my understanding, although a non-return valve would seem like the easy option, if it were safe practice.
Any thoughts?

As long as one of the pipes up to the expansion tank is clear of valves, ie either the flow or the return then the 'safety' escape route is not compromised by one of the pipes having some form of check valve. And yes I have seen a gravity check but that was a long time ago! (Actually my first house had a coal fired back boiler, a cylinder and 2 radiators, one up and one down, in 1975)

BTW could it be the heating pumped flow that is cooling the cylinder and not gravity alone?

Have a chat to a stove installer about what they normally do to stop reverse flow and cooling of the cylinder. They may have a simple ****ion.