Drain C/H system to change secondary heat exchanger on combi?

[Al D]

Hi, Is is necessary to drain a domestic C/H system just to change secondary heat exchanger on a combi boiler (Brittony 80)?

Thank you,

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[John]

Not if you can close off the system isolation valves. Then you only need to depressurise and drain the boiler

[Al D]

I can close off the system isolation valves. How do I depressurise the boiler?

Thanks again,

AL D

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[Ed Sirett]

Most combis have isolators on the flow and return connections. Follow the procedure in the manual.

[John]

If you look in the manual it should show the location of the drain point. Don't use the safety valve as they almost always get a bit of crud under the seat and will not seal properly again.

[Al D]

Yes! The manual showed a drain plug under the diverter valve, but when I looked, all I could see was solid black plastic! So I had to use the pressure releif valve - and yes, you were right: it dripped afterwards. I took it to bits and cleaned it but it still dripped! So I smeared a bit of silicone grease over the mating surfaces. All is watertight now.

Cheers,

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