Replacing a leaky Speedfit-type connector - OK to do this?

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I have a twist & lock 22mm Speedfit-type connector (though I think it's a generic brand) on the central heating system and it has sprung a small leak so wish to replace it with similar. I would grateful for comments on my plans to carry out the replacement.

The gas central heating system is based on a system boiler and is a sealed system with two expansion vessels (because the original expansion vessel built into the boiler casing didn't have enough capacity). Fortunately, the leaking connector is in the loft and almost at the highest point in the system. In fact, the leaking connector is on one of two 500 - 600 mm vertical pipe sections that have a valve at the top end and appear to be for venting air - at least that's what I used them for when venting air from the gravity CH system it once was. See photo. One of these vent pipes is on the radiators' supply "ring main" and the other on the radiators' return main.

I have little experience of pressurised CH systems/expansion vessels so I'd like to check that my repair plans are not likely to cause damage or other problems. This is what I plan to do:

1 Turn off the boiler (incl. integral circulating pump) at the mains switch.
2 Drain some water from a convenient radiator drain point until the system pressure is ??? 1 or 2 litres maybe?
3 In the loft, open the air vent in the vertical pipe to allow the water level in the pipe to reduce ??? How do I judge this?
4 Remove leaking connector. Check condition of pipes (one plastic, one copper) and clean/debur as required. Replace connector with similar new one. Can't see any branding marks on the 22mm plastic pipes or the connectors. Will any generic 22mm twist & lock connector be OK?
5 Close loft air vents and re-pressurize system to normal pressure (about 1 bar cold) using filling loop.
6 In loft, vent air from system. Repeat steps 5 and 6 as necessary.

Is this a suitable method? Appreciate any guidance. Many thanks.
 

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1 Turn off the boiler (incl. integral circulating pump) at the mains switch. Yes
2 Drain some water from a convenient radiator drain point until the system pressure is ??? 1 or 2 litres maybe? - Not needed - You could use the vent on the same pipe as the coupler to slowly release the pressure until the boiler gauge reads 0, bowl under the pipe at the bottom - Then loosen the coupler you are going to replace and let the water run out of that until it stops,
3 In the loft, open the air vent in the vertical pipe to allow the water level in the pipe to reduce ??? How do I judge this? Not required any more
4 Remove leaking connector. Check condition of pipes (one plastic, one copper) and clean/debur as required. Replace connector with similar new one. Can't see any branding marks on the 22mm plastic pipes or the connectors. Will any generic 22mm twist & lock connector be OK? you need to use the same insert in the plastic pipe as the fitting you are using
5 Close loft air vents and re-pressurize system to normal pressure (about 1 bar cold) using filling loop. Yes
6 In loft, vent air from system. Repeat steps 5 and 6 as necessary. Yes - also check the highest radiators

If it's that elbow in pic 2 then the copper pipe looks like it might actually have PTFE tape on it?? If it is, that will probably be why it's leaking.
 
Drain enough down for pressure gauge to read zero.
Open air cap ends you should be then good to go.
Just have a couple of old towels to hand.
I would personally use a speedfit connector even better tectite classic. Make sure inserts are in place.
Refill get air out pressurise to 1 to 1.1/2 bar
 
They're not speedfit fittings, but an alternative brand, what looks like ptfe is the collar of the fitting.
 
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Thanks for your replies, folks. I was wary of causing problems with the expansion vessels, having never done DIY plumbing on pressurised systems before. Thanks for the tips and good to know I'm on the right path.

They're not speedfit fittings, but an alternative brand, what looks like ptfe is the collar of the fitting.

Agreed. What looks like PTFE tape beneath the 22mm connector copper pipe end in the photo is actually a more substantial sleeve/collar of plastic - and it's quite loose - so part of the connector's release mechanism. I've checked out YouTube videos and can see how these, or similar, connectors work so should be OK using them (famous last words!).

Only issue may be that I don't know who manufactured the faulty connector (or the plastic pipe it connects) as I can't see any branding marks on connector or pipe. I can however see some embossed figures on the end of the connector's twist ring, but not clearly. These figures may become clear when connector is removed and checked under daylight. If I can't determine the connector's manufacturer, guess I'll get a JG Speedfit or Peglar Tectite Classic connector.

you need to use the same insert in the plastic pipe as the fitting you are using

Make sure inserts are in place.

I was hoping to reuse the existing plastic insert for the plastic pipe connection. Is that OK?
 

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