Combi Boiler

[Aquagility]

Since a combi boiler serves both hot water and central heating, is it possible to drain down one without the other?

[malagabob]

There should be isolating valves (more usually ends of shafts) where the flow and return circuits enter the boiler casing.
What make is it?

[Aquagility]

malagabob, I can't check on the valves until my next visit on Saturday (weather permitting!)
The boiler is a Riva Compact HE, three years old.
I've not moved in yet, and have no experience of combi's.

[The Builder]

Hot water is totally separate from CH in a combi, Aqua.

In combi hot water there is nothing to drain down. It's supplied by the mains, and heated instantaneously. There is, or course, some water inside the boiler itself. Is that what you mean?

On the CH side, radiators can be drained.

In short, either HW or CH can be used even if the other mode is not in use.

[Aquagility]

Many thanks to you both. I'm 60 years out of date!

[Dodger666]

If you drain the CH you won't be able to get hot water as the lack of boiler pressure will prevent it operating.

[Aquagility]

Good point, Dodger. Thanks.

[The Builder]

Re: Dodger's point.

There is a very simple way to have hot water with the rads drained. I'm sorry, I should have mentioned it, but I wasn't sure just how "technical" you wanted to get, Aqua ;o)

If you need to, a simple bypass loop is fitted across the radiator Flow & Return.... effectively fooling the boiler into thinking the rads are still full.

[Aquagility]

Builderman, let me explain my problem. We not only have to move a rad, we have to take it out of one position where a new wall is to be built, and put it back in another position on the new wall AFTER it has been built! The present plan is to bypass it as you suggest, and build the wall over the bypass, cutting it off later when, hopefully, it will be a little warmer and we won't need the c/h. Tricky!

[The Builder]

I should start a campaign for a "sketching" facility on Ab, Aqua. One quick glance being worth a mile of typing ;o)

Right, if I understand this, you need to isolate one rad only?
I would drain down once only, and for only a few minutes needed to fit service valves onto the flow and return pipes to the rad.

Re-fill. That way, the heating system is only briefly interrupted.
Do the works needed, fix the rad, connect to system, turn on the valves, and you're back in action.

[mrs_overall]

I have a keen interest in combi boilers. That is the only reason I am following this post, honest.
Fascinating subject.

[SlackAlice]

^^^^^
stalker! ☺

[Aquagility]

You're a clever lad, Builder. Must be, 'cos we've reached the same conclusion! I'm grateful for your trouble and advice, though.

[The Builder]

Haha. Now there IS a compliment.

You're always welcome Aqua :o)