Sanity check..., gravity hot water and pumped radiators, should they work together

[Matstones]

I hope someone can comment on my setup and let me know if I have a problem or not !

I have old gas central heating system, all was working:

gravity fed hotwater heating
radiators via pump.

We then had back boiler fitted to wood burner and replacement cylinder with 2 coil element type fitted by professional plumber, so water can be heated by gas or wood.

Can't seem to heat water from boiler

Can gravity work fast enough to transfer the heat, from cold.

When I try there is lots of scary banging and sound of water rushing through pipes, the input of cylinder gets too hot to touch, the bottom exit gets slightly warm, Water clearly not flowing through it properly.

Even with the radiators on, hot water doesn't seem to get heated, but as the pump is pulling water through radiator circuit it's hard to see why it would flow down into the hot water circuit, but no banging or venting but water does not get heated

As a layman I can think of three possibilities

1/ The water heats up too quickly to create circulation current, boils and vents off
2/ There is a Honeywell valve on exit - I replaced the head, and checked the spigot turns, this seems to be OK, and does activate when powered - and tried locked open - seems to be ok but could be blocked
3/ An air block in hot water heating element

What I want is to be able to heat water from boiler without radiators being on....

Should gravity be enough for water heating only

As there are two parallel circuits (rads/pumped+ water/gravity), it's hard to see how they can both exist together...

If you made it this far - thanks for reading - any comments very welcome

Matt

 

[stani]

You've had a motorised valve fitted to your cylinder, it is now NOT gravity.
DO NOT USE until you have got the fitter back, you are heating water against a closed valve.

 

[Chalked]

Nothing wrong with a motorised valve on a gravity hot water return.
It should be wired up as a "c plan" incorperating a white wire in the head.

 

[stani]

Your right, just never came across C plan, but do remember them.
Still, banging noises there's a problem

 

[Matstones]

You've had a motorised valve fitted to your cylinder, it is now NOT gravity.
DO NOT USE until you have got the fitter back, you are heating water against a closed valve.

When I set the controller to call for hot water it activates the valve so valve is open.

The logic being in winter we can have radiators on without the boiler heating water. The wood burner produces more than enough heat to heat the water, but only heats lounge so we need radiators on...

In summer, we want the opposite - no wood burner, no radiators, but gas heated water..

So in summer, controller calls for hot water, valve does activate, boiler heats up, after maybe 2 minutes, clanging, whoosh, and boiler turns off due to it's thermostat.
upper pipe too hot to touch, lower pipe slightly warm. I have tested with Honeywell head off and manually turned spigot anti-clockwise

Should gravity work - or do I have blockage or air lock...

 

[Matstones]

looking at drawings I do have a "C plan" system

 

[Best]

Why is the flow pipe rising from the tee to the coil?
Sorry to tell you this, but your plumber doesn't know much about pipework
Another thing is some cylinders have coils that only suit pumped water.
You have to order a cylinder that is suitable for gravity circulation that solid fuel fires require

 

[Best]

Gravity should work no bother at all and fairly fast.

 

[Chuck]

Not all cylinders are suitable for gravity-circulation systems. Most of them these days assume a pumped system. Check you've had the right type installed.

Air locks will, of course, prevent circulation but the installed pipework should have the correct gradients and vents to ensure they don't occur.

Looking at your photo. I would expect to see the hot water rise from the boiler, turn right flow down a slight gradient (your's is upward) through the Honeywell (?) valve, into the top of the heat exchanger where it transfers heat to the cylinder, cools, and emerges from the return near the bottom.

The upward gradient on the upper pipe, which you call 'return' and I think should be 'flow' would be a great place for an air lock to form.

If anything I've guessed/suggested conflicts with the manufacturer's installation instructions then I'm wrong, follow the MI!

Edit: While I was typing this Best posted essentially the same points. He was more economical with his words, and I paused to get a mug of tea midway, so he won.

 

[Matstones]

Why is the flow pipe rising from the tee to the coil?
Sorry to tell you this, but your plumber doesn't know much about pipework
Another thing is some cylinders have coils that only suit pumped water.
You have to order a cylinder that is suitable for gravity circulation that solid fuel fires require

I am not a plumber but understand the pipe has to rise for gravity to work. Around the back of the boiler (photo doesn't show) are similar 28mm pipes for wood burner circuit which works well.