Using Combi Whilst CH Drained

15 Mar 2009
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Newcastle upon Tyne
United Kingdom

I was thinking of draining the CH system down as I have a few rads and valves to change but will be doing so over a few weeks and will still need hot water.

Have read a few posts which state hot water not possible if CH drained? What if the CH flow and return valves are both closed off before the system is drained - will this allow me to continue using the hot water as essentially the combi is isolated from the CH circuit so won't matter if it's drained or not?

Hope someone confirms this is OK as have been running the combi with the CH valves closed off as recommended by service engineer to eliminate the combi as a cause of a pressure drop in the system!

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Yes, that should work. As long as the boiler is registering correct pressure (1.2Bar approx) it will operate hot water.
Thanks for reply, just worried as I'd read a lot of people saying the boiler can't be used if CH drained but nobody suggesting closing off the valves at the combi before draining!

Depends on the boiler I would say best to check with the manufacturer.

Most of the modern boilers do a pump over run to cool the applicance and heat exchanger after supplying hot water and for this to happen both the flow and return must be connected and filled.

Nothing stopping you cutting the flow and return pipes and installing some
temporary pipework.
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You did not tell us the boiler model.

Most older boilers are very tolerant of anything like this but care should be taken if its a modern premix boiler as the specific heat of the components is very low.

Hi all,

It's a baxi 105he which has been in about 6 year now.

I've not cut into any of the CH pipework yet so can easily re-open the valves if thats the best thing to do?

Just would have preferred to drain down and get all the jobs done then refill later rather than have to drain a couple of times as some of the rooms not yet ready to have the pipework done yet but suppose I could just leave the rooms that are until I can do it all at once!

Thanks again for the advice all.
I dont think you will have much of a problem with that model.

But do turn down the hot temp as low as you can live with first.


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