Gravity Circuit Issue. Advice Appreciated

[Edgy]

Hello, I've just replaced an oil-fired range with a wood burning range. I have installed a gravity circuit in accordance with the maker's spec. I have water flowing very nicely around the circuit, however, it is returning through the cold water feed rather than the gravity return as the heated water is bypassing the sink radiator and water cylinder and venting direct into the f&e. I assume this is likely to be due to an air lock in the gravity return and wondered if there was any way to remedy without draining down and refilling.

 

[Toddyplumb]

You have got something wrong with your pipe layout or falls , any chance of a picture ?

 

[Edgy]

Thanks. A picture's virtually impossible as the pipes go through a three feet thick wall and then into the eaves.

I have the gravity riser going straight up 4 metres, a 45° bend to take it through the wall with another the other side. It then runs to the top of the sink radiator on a gentle upward curve and then on similarly to the hot water cylinder before rising about two metres to the f&e. The return side runs from the bottom of the sink radiator and the hot water cylinder below the level of the "hot" side with similar 45° connections either side of the wall.

The cold water feed is also higher than the cold water return.

Hot water is teeing into the sink radiator but not returning, likewise on the cylinder.

Any help gratefully received!

 

[ecowarm]

I think a sketch might help

 

[Toddyplumb]

Witout a sketch or picture difficult , but here goes .
You have teed to the heat sink and teed to the cylinder with the feed and expansion in effect at the end of the line and at the highest point. Gravity is working as it should and is heating your expansion tank !.
Take the feed and expansion back to the boiler , I am assuming you have 4 tappings, Top 2 gravity flow and expansion / vent. bottom 2 gravity return and feed.
When ever we install expansion tanks on pumped systems we always loop under the feeds to stop gravity circ

 

[Edgy]

Thanks. When following the installation instructions I did think the hot side would take the logical route so I should, in effect loop the feed side down before rising to the f&e after the cylinder tee to encourage water to take the correct direction.

 

[Toddyplumb]

Could really do with a sketch , if you cant get them back to boiler then on gravity and as long as there are no valves then just vent on the flow and feed on the return , and yes loop under the feed

 

[Edgy]

Many thanks for your advice, I now feel confident that I'll have the system running as it should.

 

[Plucky]

How do you mean loop under the feed?

Can you provide a sketch of what you mean? I have to install a system to a woodburner with pumped heating and gravity hot water and what you are saying is making me think I have things wrong in my head.

 

[justlead1]

Hi Water will not emerge from vent under normal working temp, providing the vent is taken high enough above expansion cistern and of course its a complete gravity system and no circulating pump is included anywhere.

 

[Toddyplumb]

Loop under : instead of coming vertically off the top of the pipe with the connection have the connection vertically below the pipe then connect in and go vertical. Gravity circulation dont work downhill, not very well anyway
Just the feed mind NOT the vent

 

[Edgy]

So, in essence, I run the feed to a tee into the hot water cylinder and then drop the pipe on the other side of the tee to below the level of entry and then take it back up so hot water should go into the cylinder and will only vent under pressure from the boiler not being able to go through the cylinder? Another, probably stupid question, why can a Geminox cylinder not be used in a horizontal orientation - that would negate my need to replace the cylinder with a usual top entry and bottom exit for the gravity...?

 

[Toddyplumb]

I dont think you are understanding this. Can you attach a sketch of what you have

 

[Edgy]

Have an 04:00 start tomorrow, will do when I'm back. Thanks for your help.

 

[Edgy]

On the advice of Geminox - they tell me their cylinder will not work within a gravity circuit - I have ordered a conventional cylinder that should arrive next week.

On receipt, I will modify the plumbing laid in to the Geminox to run to the new cylinder; my experiences of last week still lead me to think that the feed from the gravity circuit needs to drop after the entry to the cylinder before rising to the f&e.

Do I need to drop below the gravity return from the cylinder?

 

[Edgy]

I have now installed a standard indirect hw cylinder and am now waiting for an immersion blanking plug...

However, I've given the system a test with a very small fire and the hot water is arriving at the cylinder - I've teed down vertically from the inlet with a loop that goes to the bottom of the coil before rising to the vent. The hot water appears still to prefer venting rather than running through the coil - I'm hoping this is due to air in the system and I'm going to run the pump on the other circuit intermittently and bleed the system whilst waiting for the blanking plug.

I have vertical rise and fall on the gravity circuit of five metres and, having gone through the wall, a rise and fall across 6 metres of approximately 60cm so can't see that it won't work...

Have I missed something?!

 

[buckley plumb]

Hi is there any chance anyone can produce a sketch of the correct way how to do a gravity hot water only with heat sink rad. i was asked to look at one last wk and the pipes from the oil rayburn come up through next floor verticaly and into cylinder cupboard and into indirect cylinder coil flow to top rtn to bottom but the expansion vent was teed into pipe entering top of cyl coil and feed teed into bottom of cyl coil .they wanted a heat sink fitting as there was never one fitted by the installer that did the goverment grant upgrade. my issue is where would i tapp the rad into and if the rad is taller than the cyl top coil entry then the rad would get all the heat flow and bypass the cylinder.

thanks ant

 

[ecowarm]

Hi is there any chance anyone can produce a sketch of the correct way how to do a gravity hot water only with heat sink rad. i was asked to look at one last wk and the pipes from the oil rayburn come up through next floor verticaly and into cylinder cupboard and into indirect cylinder coil flow to top rtn to bottom but the expansion vent was teed into pipe entering top of cyl coil and feed teed into bottom of cyl coil .they wanted a heat sink fitting as there was never one fitted by the installer that did the goverment grant upgrade. my issue is where would i tapp the rad into and if the rad is taller than the cyl top coil entry then the rad would get all the heat flow and bypass the cylinder.

thanks ant

Google Image Result for http://www.theagashop.com.au/images/rayburn/technical/raychsystem4802.jpg

 

[buckley plumb]

thanks for that .it looks like the radiator must be lower than the cylinder coil then.is that correct of can the tappings just be situated lower

thanks ant

 

[Edgy]

Have now been trying to get air out of the gravity circuit for some time...

Bosky's installation schematic shows cold feed directly next to the boiler but, having had the system working the wrong way, a common return and feed closer to the hw cylinder seems to make more sense.

Any advice, please!

 

[ecowarm]

Have now been trying to get air out of the gravity circuit for some time...

Bosky's installation schematic shows cold feed directly next to the boiler but, having had the system working the wrong way, a common return and feed closer to the hw cylinder seems to make more sense.

Any advice, please!

You need to follow manufaturers instructions

 

[Edgy]

OK, so I have done everything by the book, all angles, connections &c are as they should be.

Heat reaches the hot water cylinder intermittently and the heated water still favours the pumped circuit, when the pump is not running.

To enter the pumped circuit, the heated water has to loop below the gravity pipe (that runs vertically directly from the outlet) and then rise to the first floor radiator before dropping back to the ground floor to one radiator. The radiator is very hot.

When the pump isn't running, water circulates around the pumped side and eventually rises in the cold water feed from the loft tank...

I have no idea why the heat isn't following the gravity circuit and cannot understand why it will follow a less favourable route, gravity-wise.

In the installation initially the circuit worked albeit it bypassed the hw cylinder (designed for a pumped circuit & that I have now replaced with a standard cylinder) and circulated via the f&e running back on the cold water feed rather than the gravity return; the gravity return and cold water feed are at the same level.

Any advice, please. I would like a bath and this is taking over my life.

 

[Toddyplumb]

You are gonna have to post some pictures or some sketches of exactly what you have
We might be able to sort it in a few minutes then

 

[Edgy]

Thanks, here are pictures; the heated water is favouring the pumped side - going down rather than up the vertical pipe and the pipe it follows then goes up the the first floor before coming back down to the same level to heat another radiator.

 

[Toddyplumb]

My first response is Its never gonna work , If anything its working backwards when return heats up. Im going for a drum lesson now Ill have a better look later. It doesnt look good !
Picture 1 is the top T the gravity flow going up ? The swept T branch the gravity return ?
Where is your open vent ?
How are you supposed to vent the cylinder coil ?

Now I really have 2 go

 

[Edgy]

The 28mm on the top t is the gravity going up and gravity return is the 28mm pipe on the bottom swept t...

Open vent is after the loop on the cylinder feed and one metre above the cylinder and I've vented the coil by loosening the inlet...

It worked when first fired up but bypassed as the cylinder as it was for a pumped system and so circulated via the F&E running from the vent to the cold water feed - obviously not good. So, I replaced the cylinder and can't get heat consistently to it.

I forgot to mention, the installation exactly follows the layout provided by the manufacturer. I drained down and refilled and now the gravity feed gets hot to about 8 feet then stops, circuit is full and no apparent air

 

[Toddyplumb]

At the cylinder cut out the looped under feed .
Fit a new T pointing up and take a vent above F&E tank
On the cylinder return fit a T pointing down
Connect the looped under feed to this return feed

As it is it will not vent

Just check all the pipework is rising , where the cylinder flow comes through the cladding it looks like its falling !
If this works then start supporting , clipping and lagging that pipework !

 

[Edgy]

Thanks, I'll do that - just being a bit thick though - if I take out the looped-under feed, where do I take the pipe back to the return side from the looped-under feed?

Pipe definitely rises from the cladding (I see what you mean - it's a 45° angle and it does look like it's falling in the photo but it isn't!) and cylinder inlet is a couple of inches above the top of the heat sink radiator.

 

[Toddyplumb]

Anywhere on that straight section of pipe from cylinder return to the wall

 

[Edgy]

Many thanks - nearly there now. Hot water reaching the cylinder but going no further (apart from via the vent) so checked all pipes and found a problem where the 28mm passes through the wall (the wall's three feet thick and under the edge of the roof so it wasn't the simplest of tasks). The 45° bend had been moved 18 inches into the wall and pushed up so giving a rise on the return of about six inches, hence the water wasn't returning. So, I'm draining down again and will let a piece of pipe in to place the angle where it should be and shorten the vertical return accordingly.

It should work then!

Thank you again for your help, I wouldn't have found this problem if I hadn't solved the first one with your advice; am I able to contact you direct, I'd like to send you something for your help?

 

[Toddyplumb]

Just pleased you got it sorted Just confirm that it does work correctly when you have sorted that last pipe.

 

[Edgy]

All fired-up and water is heating, some heat is bypassing the cylinder via the loop to the return (which I assume is normal) and the circuit hasn't yet got up to return temperature to activate the pumped circuit so I do believe it's working as it should.

Thank you again for your help, it is very much appreciated.

 

[Toddyplumb]

Nice one

 

[Edgy]

First hot bath in six weeks without using a kettle!