Airlock in HW Cylinder Gravity Fed Open Vented HW/CH system

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I don't think that you have an air lock. From your diagram to me it looks like the system is lacking in
"Circulating Head".
You could try turning the speed on the pump up, however, I don't like that combined cold feed and expansion idea in connection with this.
You could also gain a bit of CH by levelling out that primary flow by taking out that drop in the flow pipework.
The modern solution would be to convert to a pressurised system by removing the expansion tank and fitting an expansion vessel in its place.
servotech,
 
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Zone valves must be latched open whatever route you choose (that's why that facility is on them, for filling the system), that HW zone valve should be repositioned ASAP, presently, if CH only on then the only expansion/vent path is back through the return through the HW coil via its gate valve (tie wrap this fully open, as a temporary measure). My 50 year old oil fired system is similar to yours and on the very rare occasions I have fully drained it down, I latch the zone valves open and I just barely open a service valve that I installed on the F&E tank cold water supply. You can just drain the system down again to the gate valve and then with both M.valves latched open just allow a trickle of water into the F&E tank until "full", that will IMO do the trick since the CH system is OK.
You could syphon or bale out the 5/10 litres of water in the F&E tank, you only then have to drain off a few litres at the gate valve, less of a mess.

Post #13 suggestion would probably work OK but I wouldn't like taking the risk of pushing any sludge which may be in the bottom of the rad(s) elsewhere.
Thanks for your suggestion. When you say reposition the h/w zone valve are you meaning to physically change the position it is installed? Where else would it go as I assume it should be on the feed pipe going to the cylinder? If I had to drain the system I did consider syphoning off the water in the tanks as I have a wet/dry vac that should be able to do the trick. It is a bit tight getting to these tanks as they are located with the boiler in an airing cupboard. I'm assuming I need to shut off the mains water supply when draining? When refilling are you suggesting I slightly open the mains water to fill the tanks? Will this not create the airlock again or are you saying with the system drained and with the zone valves open the air has a way of escaping through the vent pipe above the f&e?

I did also think about the risk of shifting the likely sludge in the bottom of the first radiator when filling back up through the drain cock.
 
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Re position it as shown.
Shut off mains water yes, drain F&E tank only, shut the gate valve, open compression nut above the gate and drain down the remaining few litres, re tighten compression nut, open gate valve fully, latch open both zone valves, then just (barely) crack open the mains, this will/should allow the air to vent and the water to flow downwards in the same pipe(s), has worked very well for me, only real difference is that my combined vent and cold feed are right up at the tank but should still work OK in your system.
 

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If I read your suggestion correctly you are basically saying to not drain the system but rather skip that and fill from the drain cock. Instead of refilling from the feed side you are suggesting leaving the zone valves closed and filling the system from the return side via the c/h? This will force the airlock to shift out of the cylinder and assuming into the air vent?
yes with the zone valves closed, you want the mains water to enter the coil via thereturn an push any ait into the expansion pipe
 
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Re position it as shown.
Shut off mains water yes, drain F&E tank only, shut the gate valve, open compression nut above the gate and drain down the remaining few litres, re tighten compression nut, open gate valve fully, latch open both zone valves, then just (barely) crack open the mains, this will/should allow the air to vent and the water to flow downwards in the same pipe(s), has worked very well for me, only real difference is that my combined vent and cold feed are right up at the tank but should still work OK in your system.
Understood about the zone valve for h/w although the horizontal leg in real life this is only about 10cm long. The diagram placement of items made it difficult to represent that properly.
I don't think that you have an air lock. From your diagram to me it looks like the system is lacking in
"Circulating Head".
You could try turning the speed on the pump up, however, I don't like that combined cold feed and expansion idea in connection with this.
You could also gain a bit of CH by levelling out that primary flow by taking out that drop in the flow pipework.
The modern solution would be to convert to a pressurised system by removing the expansion tank and fitting an expansion vessel in its place.
servotech,
I should explain that the pipe work for the h/w is short in distance as everything is located in the airing cupboard. The height from the floor to the cylinder connections is about 1-1.5m. The c/h works fine and the overall distance of all the radiators is much longer. The pump is set to speed 3 which is the highest.
 
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Understood about the zone valve for h/w although the horizontal leg in real life this is only about 10cm long. The diagram placement of items made it difficult to represent that properly.

I should explain that the pipe work for the h/w is short in distance as everything is located in the airing cupboard. The height from the floor to the cylinder connections is about 1-1.5m. The c/h works fine and the overall distance of all the radiators is much longer. The pump is set to speed 3 which is the hig

The only air vent is the overhanging vent above the f&e tank pointing downwards. Other than that there is no other air vents I can find. The gate valve is open as you turn it anti-clockwise. It also stops and doesn’t continue turning.
I'm surprised the coil is airlocked, positioned as it is very close to the flow&return piping, are you absolutely sure that the gate valve is open, if it is, then you should get ~ 3 to 4 full turns clockwise before its fully closed and visa versa to reopen.

The M.valve can be re positioned on the vertical return leg (again, ensure it already isn't), just ensure the arrow on the valve body is pointing downwards in the direction of flow.
 

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When the plumber changed the h/w actuator he drained the system from the compression joint on the boiler side of the gate valve. The only way the system would have drained would have been if the gate valve was open. It was also dripping afterwards as the compression nut needed tightening.

Also the cylinder isn’t stone cold. It does get a bit warm but the boiler shuts down because the water isn’t circulating. At one point after the actuator was replaced, the feed pipe to the cylinder remained cold and the boiler shut off sooner. I manually moved the valve behind the actuator and heard a slight sound. After that the pipe started to get hot and the cylinder lukewarm.

Is there a way to test the gate valve apart from the turns?
 
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I would think that if the gate valve wheel is turning 3 or 4 turns between fully open and fully shut that the valve gate is moving up and down inside the valve and therefore clear, to be sure you could drop the level below the valve level and remove it for inspection/renewal.
If the boiler is firing up each time you request HW only then the valve actuator must be moving and presumably the valve spindle, you can latch the (HW) M.valve open, then fire up the boiler on CH and see if the cyl coil flow and return
pipes at the cylinder are hot, if very poor circulation then the flow (top) pipe will be very hot and the return only lukewarm.

What make/model circ pump is installed?.
 
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Zone valves must be latched open whatever route you choose (that's why that facility is on them, for filling the system), that HW zone valve should be repositioned ASAP, presently, if CH only on then the only expansion/vent path is back through the return through the HW coil via its gate valve (tie wrap this fully open, as a temporary measure). My 50 year old oil fired system is similar to yours and on the very rare occasions I have fully drained it down, I latch the zone valves open and I just barely open a service valve that I installed on the F&E tank cold water supply. You can just drain the system down again to the gate valve and then with both M.valves latched open just allow a trickle of water into the F&E tank until "full", that will IMO do the trick since the CH system is OK.
You could syphon or bale out the 5/10 litres of water in the F&E tank, you only then have to drain off a few litres at the gate valve, less of a mess.

Post #13 suggestion would probably work OK but I wouldn't like taking the risk of pushing any sludge which may be in the bottom of the rad(s) elsewhere.

I missed this one.
Johntheo5 is spot on!
If that diagram is correct, and that HW MV ever shuts off the whole system then becomes a bomb.
#1 Priority ASAP to move it.
Surely no one fully qualified in plumbing will have done this.
 
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The circulating head is measured from the base of the heating expansion tank to the centre of the heat exchanger in the cylinder which must be very low with everything in the airing cupboard and that high loop in the flow reducing the head even lower.
Check that air is not being pulled in from that expansion pipe with the pump on 3 it will be far easier for the pump to favour this over circulating the water in those primaries.

Conversion to a pressurised system looks to be the only cure for me. However, you must get that motorised valve positioned changed before you do anything else.
 
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i appreciate all the advice you all have already given. Honestly the amount of information you all have shared has been invaluable.

So I checked the gate valve is working as it does turn 3-4 times both ways and you can feel the water passing through the return pipe.

The system did have a certainly amount of air in it. I had to bleed the the first closest radiator to the boiler initially today which eventually stopped. After then turning on both the central heating and water at the same time i heard strange noises from the boiler and pipes as if water combined with air was passing through the system to the central heating side. I then tried to bleed the radiator again and to my surprise it started airing again. All in all i probably had to bleed it 4-6 mins until we had water come out. It was probably the most amount of air I’ve ever had to bleed in a radiator. I noticed that with all the air being released the tanks and the same time were filling up with water even though were were not using any other water in the flat.

The boiler seemed to calm down and the hot water seemed to be a little more warmer, but certainly there was a clear difference between the red hot feed and a lukewarm return. The boiler was turning on and off a lot more but probably because the central heating was on with both valves open.

Unfortunately i discovered the drain cock wasn’t working as the inside mechanism was stuck shut while the outer screw on part came away. I didn’t want to attempt to do anything with it in case this created more problems that couldn’t rectify. I wasn’t sure I wanted to attempt to install a screw on drain cock which I’ve seen online. I’m not sure this is a great replacement for the existing drain cock.

There was certainly more swishing and whooshing from the system and gurgling.. but still no joy with the hot water being hot as you would expect.
 
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The make and model of the pump is TSG CP53. It is on speed setting 3. You can feel the vibration on the return pipe when the pump is on.
 
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i appreciate all the advice you all have already given. Honestly the amount of information you all have shared has been invaluable.

So I checked the gate valve is working as it does turn 3-4 times both ways and you can feel the water passing through the return pipe.

The system did have a certainly amount of air in it. I had to bleed the the first closest radiator to the boiler initially today which eventually stopped. After then turning on both the central heating and water at the same time i heard strange noises from the boiler and pipes as if water combined with air was passing through the system to the central heating side. I then tried to bleed the radiator again and to my surprise it started airing again. All in all i probably had to bleed it 4-6 mins until we had water come out. It was probably the most amount of air I’ve ever had to bleed in a radiator. I noticed that with all the air being released the tanks and the same time were filling up with water even though were were not using any other water in the flat.

The boiler seemed to calm down and the hot water seemed to be a little more warmer, but certainly there was a clear difference between the red hot feed and a lukewarm return. The boiler was turning on and off a lot more but probably because the central heating was on with both valves open.

Unfortunately i discovered the drain cock wasn’t working as the inside mechanism was stuck shut while the outer screw on part came away. I didn’t want to attempt to do anything with it in case this created more problems that couldn’t rectify. I wasn’t sure I wanted to attempt to install a screw on drain cock which I’ve seen online. I’m not sure this is a great replacement for the existing drain cock.

There was certainly more swishing and whooshing from the system and gurgling.. but still no joy with the hot water being hot as you would expect.
Apart from any safety implications not life or death just now as the expansion is open to atmosphere as long as the gate valve is tie wrapped fully open, but only as a temporary measure, you will never get rid of the air except that the HW zone valve is re positioned as suggested as the vent is just that and must always be open to atmosphere.
You might also install a air vent (either auto or preferably, for me, a manual type), you may be able to T it in on that short 10cm leg into the cylinder coil.
Also suggest running that 5M pump on speed 2, can't find any pump curves, I am running a 12 rad system for 50 years at a equivalent 3.5M head which your pump should deliver at the above speed.
Get someone to watch the vent for a spurt of water when the boiler starts and also when it stops, also hold a "glass" of water with the vent immersed in it and see if the level changes with CH only, HW only & CH+HW on.
 
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is there a gate valve on the return from the cylinder good chance he has snapped that in closed position
 
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is there a gate valve on the return from the cylinder good chance he has snapped that in closed position
Don't think so, post #26.... "So I checked the gate valve is working as it does turn 3-4 times both ways and you can feel the water passing through the return pipe."
 

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