Another jammed stopcock question

[Vicario]

I tried to turn my main stopcock (under the sink) and it is impossible to move. I am hoping to have a new electric shower installed and I assume that the mains will need to be off when the plumber comes - I don't think that there's any other way to isolate it, is there? Anyway, I've watched every YT video on this subject - use WD40 first/no, don't! Twist the spindle with a wrench/no don't!, Tap the top with a hammer/no, don't!, Loosen the gland nut first/no don't!/, (check you know how to isolate in the street before touching it/no need!), Warm with a hairdryer first/no need! Shall I continue? Please can the guys on here give me a definitive plan? Or shall I just get someone in? Seriously though, thanks in advance.

 

[johnny2007]

From experience: WD40 helps and so does releasing the gland nut slightly.
Spray the WD40 over a couple of days and see if the stopcock moves.
However, WD40 might penetrate in the water (maybe?), so good flushing needed after.

 

[Old Salt]

Stop cocks etc should be turned back half a turn after opening so that they dont jam open. It also aids identifying which way to turn to close it.

I know this doesn't help you but it may save problems in the future.

 

[foxhole]

You should find plumbers are pretty experienced at turning off water supply.

 

[oldbuffer]

1. There is likely to be a stop cock between the water suppliers pipes and the run to your property, usually situated just inside your boundary. Particularly likely if you have a water meter.
2. It is generally possible to freeze the cold mains pipe. However, you need to let the plumber know if your are unable to stop the water, so that he / she can find an alternative method.

 

[evdamadiynot]

I have a little dropper bottle with a mix of 75% acetone 25% sewing machine oil
It will free off stuck and corroded fixings that wd40 wont touch..