correct way for refilling the cold tank

[oldashdale]

I live in a chalet bungalow. Some years ago when I had a new boiler fitted, the installers draining my cold tank and refilled the system afterwards without any problems.

Three times in the past couple of years I've drained the cold tank myself, twice when I replaced a different tap washer and once for some other reason, I forget what. Each time I've refilled the cold tank, I've somehow created airlocks in the hot water pipes and had to do the recommended trick of connecting the hot and cold feeds to the washing machine and using mains pressure to shift the airlock. But I shouldn't have to do this every time, should I? I'm clearly doing something wrong when I refill.

I've tried various sequences of shutting the taps off upstairs and downstairs during refill but to no avail, the airlock appeared each time. On two occasions I had drained the hot tank at the same time as the cold tank but I can't remember about the third occasion. If I didn't, or if it was only partially drained, I still got the airlock.

So can somebody tell me the correct procedure?

 

[seco services]

Have you tried leaving the taps open slightly while filling and shut each tap when they start to run. this way the air has somewhere to escape while filling.

If you fit isolation valves to each tap then you have no need to drain system.

 

[Space cat]

But I shouldn't have to do this every time, should I?

No you shouldn't!

I'm clearly doing something wrong when I refill.

No you're not. Somebody did something wrong with your plumbing. My guess is that there's a slight uphill run of pipe coming off your cold tank before it turns downwards to the base of the hot cylinder. This will leave a column of air trapped in the vertical section when you refill and it will stay there until you blow it out from below - as you've had to do three times already.

Might I suggest that the boiler installers didn't drain the cold water tank but a smaller header tank. With an indirect cylinder there's no need to drain the main tank before you work on the heating system.

 

[PlumbGas]

Stop draining the tank each time, either as already said fit isolation valves to each outlet or a gate valve (Pegler) on the cold feed from the tank to the cylinder and the cold feed from the tank to the cold outlets or just bung the holes with a rubber bung, you can buy bungs from any merchant, very cheap.

 

[Space cat]

--fit isolation valves to each outlet or a gate valve (Pegler) on the cold feed from the tank to the cylinder and the cold feed from the tank to the cold outlets --

Excellent advice. Maybe you have some already. These will allow you to work on your hot water system (and tank-fed cold taps) without draining the tank at all.

In my experience, gate valves don't always close completely so you're left with a dribble, which is really bad news if you're trying to make soldered joints. I've also had one break internally leaving the thing jammed shut. I had to unscrew the entire valve head to get the broken bit out. The thing is still in the pipe with its spindle connected to nothing waiting for me to replace it with a proper stopcock.

PS: If you don't have a stop valve between the cold tank and the hot cylinder and you're about to fit one, look for - and eliminate - any uphill sections of pipe while you're at it.

 

[PlumbGas]

--fit isolation valves to each outlet or a gate valve (Pegler) on the cold feed from the tank to the cylinder and the cold feed from the tank to the cold outlets --

In my experience, gate valves don't always close completely so you're left with a dribble, which is really bad news if you're trying to make soldered joints. I've also had one break internally leaving the thing jammed shut. I had to unscrew the entire valve head to get the broken bit out. :

Thats why i specified Pegler, you'll never have a pegler brake or not work, also all gate valves should be opened all the way and then back half a turn to prevent sticking