Drain combi to repair leaking plastic pipe joint

[jonfrank]

Had a combi (Viessmann 100) fitted last year, and the plumbers directly connected the mains cold and the DHW feed to two existing plastic flexible pipes, which run up into the loft and then down behind the bathroom wall to the shower. (Before combi boiler days they were connected to a shower pump.)

There is a leak in the loft where there is a join in the plastic piping (on both pipes, as it happens) - they've been leaking for years but plumber thought he'd fixed them when fitting the boiler. No such luck.

Given no isolating valves at the boiler end of the pipes I'm staring at a wet loft (and below) unless I'm careful.... Here's my plan:

1. switch off mains water stopcock
2. switch off DHW feed at the boiler
3. open a hot and cold tap to relieve pressure in both circuits?
4. remake the joins in the loft
5. switch everything back on again

I'm only used to having worked on our old conventional boiler, so I want to make sure I'm doing it right for a combi... is there anything I need to be careful of? How do I make sure that it doesn't try to switch on while the water's off - just switch off the electric switch to the boiler??

Any suggestions / warnings appreciated. Thanks all

 

[BoxBasher]

1. Yes

2. No need to switch of feed, just turn the boiler off (should have an off switch/ no CH or DHW)

3. Yes, and to drain any pipework above.

4. Yup

5. Easy