by sparx »
Tue Mar 10, 2009 8:17 pm
Hi, did this some years ago by putting second boiler across flow & return of first one with 2 tees .
Added 2 two port valves, one in each boiler flow leg with selector switch (2 way 10Amp light switch) with mains on common and L1 or L2 to call whichever valve was needed, used valves switched output live to call original boiler or new one (which also had new pump in line), been working that way for a long time without problems,
regards SPARX