Simple Gravity System - Mega Headache

dawnwarddimond · 14 Dec 2012

Hi, can anyone help as have a problem that is now driving me mad. Feeder tank is back filling both from vent and out feed. Hot flow is going backwards, through cold feed, but by passing cylinder. I have put in a very simple gravity system for hot water off a Rayburn. The feed from the header tank goes into the return via a tee on the lower part of the coil in the hot water tank. Open vent off a tee on the flow as it goes into the tank. The flow into tank is from top exit from Rayburn, return into lower pipe. I have put in automatic vents by boiler and by tank. What have I done wrong????

transam · 14 Dec 2012

Just out of interest were is the cylinder in relation boiler , next floor up ? beside the boiler ??

doitall · 14 Dec 2012

Post an as fitted drawing should show the installation fault.

Markerpen · 14 Dec 2012

Bit more info req'd. Are you saying that water is coming out of the open vent pipe into the tank, and coming back up the cold feed at the same time?
What size pipework have you used?
How many bends/elbows are there on it?
How high is the cylinder in relation to the Rayburn?
How high is the tank in relation to the cylinder?

Nige F · 15 Dec 2012

dawnwarddimond said:
I have put in automatic vents by boiler and by tank. What have I done wrong????

probably that -

You shouldn`t need any auto/manual vents anywhere - it all should vent to F+E tank because the pipes rise correctly

dawnwarddimond · 15 Dec 2012

OK, here's more info

The rayburn is on the ground floor, hot water tank is on the second, feed and expansion above the hot water cylinder.

Bottom of cylinder is about 3m above bottom of rayburn, bottom of F & E tank is just over 1 m above the top of the cylinder coil. Open vent pipe is just over 1/2 a meter above water level in F & E tank.

There is about a 10m run from Rayburn to cylinder in 22mm piping, so just at the limit of acceptable (run is lagged). The pipes do go down to the floor before they then continually rise.

There must be around 7 bends from rayburn to tank.

The very first time it was run, about 2 weeks ago, it worked great, loads of hot water.

It was drained to fix a couple of leaks and since then it has been a real pain. The lower return pipe out of the rayburn gets hot before the top flow pipe. The hot water then travels backwards to the cylinder, but not into the cylinder, but up to the F & E tank through the inlet. When it got really hot, it travelled up the hot flow pipe and out the open vent.

The air locks, at the rayburn and cylinder have been put on since to try to illiminate air, which I though was the most likely cause.

I have threatened it with a big spanner tonight

matt1e · 15 Dec 2012

dawnwarddimond said:
There is about a 10m run from Rayburn to cylinder in 22mm piping, so just at the limit of acceptable (run is lagged). The pipes do go down to the floor before they then continually rise.

No good the pipes should be 28mm minimum and rise continuously

dawnwarddimond · 15 Dec 2012

Rayburn say 22mm pipe is ok.

Yes everyting I have read says it needs to rise continuously too. However the return, cold pipe also goes down to the floor first, so why will it rise up that one, and how did it work fine once?

matt1e · 15 Dec 2012

dawnwarddimond said:
Rayburn say 22mm pipe is ok.

For gravity hot water? I doubt it mate
what do the installation instructions say?

Matt

Onetap · 15 Dec 2012

dawnwarddimond said:
Feeder tank is back filling both from vent and out feed.

It can't, if the system is full of water.

It may be there is an air lock, an air bubble trapped somewhere that expands as the water heats up an pushes water out of the OV and the cold feed pipes.

dreadnoughtheating · 15 Dec 2012

Pinholed coil in cylinder? just a thought.

Dreadnought

dawnwarddimond · 15 Dec 2012

Pinholed coil in cylinder? just a thought.

I hope not as cylinder is new, I think your right onetap, an airlock, but if so the bugger won't get out! Drained, refilled several times, flushed with mains pressure too.

matt1e · 15 Dec 2012

Not installed correctly is my guess
22mm primary's with vertical runs that also drop into the floor first hardly promotes gravity circulation

doitall said:
Post an as fitted drawing should show the installation fault.

Any chance dawnwarddimond?

dawnwarddimond · 15 Dec 2012

Not sure how to do that, but will have a look tomorrow. It falls from the outlets on the rayburn, to the floor, so a couple of feet, I guess that is going to be a big hinderance to the gravity feed.

matt1e · 15 Dec 2012

dawnwarddimond said:
Not sure how to do that, but will have a look tomorrow. It falls from the outlets on the rayburn, to the floor, so a couple of feet, I guess that is going to be a big hinderance to the gravity feed.

It's a huge hinderance, as the flow has to exit from the heat source higher than the return for circulation to start,
you have in effect brought the pipes down and levelled them off together in the floor ( or the return may be in fact sitting slightly higher even)
There's certainly no circulation at the moment and the use of 22mm doesn't help
It's just sitting boiling its nuts off

Matt

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Simple Gravity System - Mega Headache

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