Heating Diagram for two boilers on two different phases.

[Ukraine Electro]

Hi Everyone ,i need a advise please:basicaly i got two system boiler with one imersion heather ,they must be combinet in one way.If in any reasone boiler number one lost power ,boiler two supposed start working ,two boiler on different phases .
please if any one had simillar situations ,any advise help
my idea to use fan isolator swithces ,if client have lost heating or water ,they can swith off boiler number 1 isolator and swithc on boiler number 2 isolator.then he. knows he got problem with boiler number 1

 

[pc1966]

Is there a danger of both are on at once?

Must the change-over be automatic?

A diagram would help a lot!

 

[Simon47]

A lot depends on what controls you have, the size of the boilers relative to load, etc.
If it's as simple as "either boiler is sufficient on its own" then it's simpler than if you need progressive operations (i.e. both boilers need to run when there's a lot of load). It also makes a difference if you need boiler 2 to run if boiler 1 "fails" vs simply switching over if the power to boiler 1 fails.

For the simple case where you have a basic "run" signal and only want to run boiler 2 if power to boiler 1 fails, then :
Use a 2 pole changeover relay with coil rated to the supply voltage of boiler 1. Wire its coil across the supply to boiler 1 so it will hold in all the time boiler 1 is powered. Wire the external controls to give a volt free contact when demanding (use another relay if necessary), and wire these to the common contacts of the relay. Wire the normally open contacts to the run terminals of boiler 1, and the normally closed contacts to the run terminals of boiler 2.

Whenever power is available to boiler one, the external controls will be passed through to boiler 1. If power fails, the external controls will be disconnected and re-routed to boiler 2 as the relay drops out.