Connect 2 heating controllers to one boiler

Question

I have 2 heating systems:

And I have one boiler for the whole house.

I want to connect both systems to the boiler.

My options:

Connect both of them to the boiler so that they can switch it on according to each own's programming. Is this possible? This would be ideal because it's the most straightforward but I do not know if this is possible and/or safe.
Connect the Drayton to the boiler and use one of its zones to turn the hot water on. This has only the problem that the 2 system must be in sync or I risk to burn the underfloor heating pump if it goes on while the hot water valve feeding the secondary system is closed.

Any Ideas? Suggestions?

Solar Mike · Accepted Answer · 2019-06-01 15:44:52Z

1

You can use two relays (or even diodes) so that each controller can fire the boiler without any backfeed issue between the controllers.

I would use two relays personally as they are easy to replace.

Make sure the relays are rated on both sides for the voltages used - what the boiler needs and what the controllers supply...

answered Jun 1 '19 at 15:31

Solar Mike

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I thought you couldn't use diodes (instead of adding relays) in an AC system since it would clip the waveform and basically convert it to half wave DC, or am I wrong? – Dotes Jun 2 '19 at 18:16
@Dotes depends what the signal voltages are... some are 12V DC others are mains... You need to know before you start playing. – Solar Mike Jun 2 '19 at 18:17
That makes sense, thanks! – Dotes Jun 2 '19 at 18:20

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