Getting rid of airlock in Hot Water Cylinder Coil

I have an open vented gravity system with no zone valves and a pump for Central Heating side only.

There are 2 tanks in loft, one is a cold water tank and the other a feed and expansion tank. Each of them have a vent pipe.

The boiler fires up when I switch on CH setting, but hot water cylinder tank is cold.
On HW only setting, the boiler does not fire up at all.

I suspect the Hot Water Cylinder Coil has an airlock.

I have attached a mains connected hose to open vent pipe on the Feed and Expansion tank and waited 30 mins. There were air bubbles at the bottom of the tank and I thought this would get rid of the airlock but doesn't seemed to have worked.

Any thoughts, Should I have waited longer than 30 mins ?

Thanks
J

 

Any recent plumbing work been carried out and somebody forgot to open a valve afterwards or the valve is broken and now will not open?

 

If the top coil fitting has any compression fittings close, try loosening one of these in the hopes of getting air out. I would personally avoid the actual tank connection as a loosening point as its relatively easy, depending on construction, to create more problems.

 

If the boiler doesn't fire up at all, it would suggest an electrical fault/wiring issue to me.
If the only fault on a gravity hot water system was an airlock, you'd expect the boiler to fire until its internal thermostat was satisfied (which wouldn't be long due to lack of circulation).

 

It is an old system, I have checked the valves - nothing is closed.
I have kept the HW only setting on all day today and noticed that the boiler does fire up every 3 hours or so but then switches off after about a minute even though boiler stat is set to very high position.

I will get a plumber to open the coil fittings near the cylinder however I am surprised that fitting main pressure hose to a F&E vent pipe could not push the air out.

 

Air will compress before the water shifts. I would shut off the C/H on each rad valve -not the lockshield- and one valve on the pump. Then back feed the mains to the boiler through the boiler draincock. That should shift the air by the water rising from the bottom of the system. IF you can't let it out by the coil

 

Put a hose on the c/h drain cock (use a jubilee clip to secure hose) open drain cock and back fill system using mains water, 10 seconds should be enough if its a airlock.

 

Does the boiler fire and stay on for CH? I would check this before going any further... Yes, it will make your house even warmer with this current weather we're enjoying but I'd do that to make sure the issue isn't elsewhere!

 

It depends where the open vent and cold fill are located. If the open vent is on the flow between boiler and pump, and the cold fill on the return (most likely is on an old system) it might work, but you need to close one of the pump valves and a boiler iso valve, otherwise the water can go through the rads and boiler, not the cylinder coil. Boiler isolation depends on pipework layout and whether valve(s) are installed.
If the cold fill is on the flow, just after the open vent (the modern arrangement) the water goes down the open vent and straight up the cold fill, so doesn't do any good.
Wherever you inject water, don't forget it will end up in the F/E tank. So make sure the overflow is OK, and keep an eye on it. If the tank overflows in the loft you'll have a right mess!

 

you dont force the mains water through the vent in the f&E tank, you force it through the feed and force the air out of the vent

 

OP was talking about putting water in via the open vent, and it could work, depending how the system is arranged and what valves are installed. I agree with easyflow that it's better to connect the hose to the boiler drain point, or a drain point on the return pipework, which is equivalent to connecting to the feed, if the feed is on the return. It still needs valves in the right places to make sure the purge water goes where it's wanted.
If the cold feed is on the flow, it's hard to see how you would connect the hose to that, maybe reach into the F/E tank and shove the hose over the outlet.
In any case, once air has been purged any more water going in must end up in the F/E tank, there's nowhere else for it go. That's why I suggested a bit of care.

 

its not rocket science you get a hose pipe and hold mains pressure into the feed part of the f&e and wait untill you get a steady flow from the expansion

 

No valves according to OP...

 

I assume OP means no motorised zone valves, not manual iso valves. There'll be pump iso valves for a start.

 

OK could be done, I know it's not difficult but that's likely to be a 2-man job. And if it is piped the modern way, boiler - open vent - cold feed - pump it doesn't work as if you connect to the vent or the fill it will come out of the other. It's not likely it's piped like that on an old system but it might have been modernised.
Putting mains water into a connection somewhere and giving it a splurge might work, but all I was saying was if it doesn't, need to put a bit of thought into how to send the water through the coil where you want it.