Draining down an unvented system to change rad valves

My sister wants a new towel rail fitted in her shower room so need to drain system down and change valves etc. I’ve done this plenty of times on a vented system and a system with a Combi boiler.

The plumbing set up she’s got is in the photos above. Would it just be the same as draining down the system if you have a Combi boiler I.e. turn off boiler, let water out through drain off and re fill via filling loop?

Thanks in advance!

If anyone could provide their insight by tomorrow morning, that would be grand!!!

chris_o said:

View attachment 160293 View attachment 160293 View attachment 160294 View attachment 160295 View attachment 160296 View attachment 160297 My sister wants a new towel rail fitted in her shower room so need to drain system down and change valves etc. I’ve done this plenty of times on a vented system and a system with a Combi boiler.

The plumbing set up she’s got is in the photos above. Would it just be the same as draining down the system if you have a Combi boiler I.e. turn off boiler, let water out through drain off and re fill via filling loop?

Thanks in advance!

Click to expand...

Yes treat like A combi system .

chris_o said:

Would it just be the same as draining down the system if you have a Combi boiler I.e. turn off boiler, let water out through drain off and re fill via filling loop?

Click to expand...

Yes but before turning off the boiler ,write down any existing stored fault codes .
When the boiler has cooled down,turn off the boiler electric supply and start draining down. Set the two zone valves to manual and open the thumbscrew manual air vents (above boiler&cylinder primary flow pipe) to assist in water removal.

Do your tower rail alteration. Tighten the thumbscrew manual air vents.

Add inhibitor,refill & bleed air from the system ,use the thumbscrew manual air vents to let more air out. The filter may have an air release valve,Get the pressure at 1 bar. set the zone valves to automatic.
Turn boiler electric supply back on,ensure the boiler goes through the "air purge mode" it will display a code (see manufactures instruction book). Raise water pressure to 1.5 bar.

Check for leaks,check radiators for air,check all radiators heat up and thats about it.

Before removing the top of the filter mark cap and base with alignment mark as if it does not go back exactly as it was they tend to leak .

Cheers guys, all drained and re filled with towel rad fitted and no issues. My main concern was the unvented hot cylinder and if that had any affect on the central heating, but obviously not!