2 MAINS 1 WON'T HEAT ALL THE WAY

COOT

WE REPALCED A WEIL MCLAIN LGB 6 WITH AN EGH105. THE 105 IS SIZED TO THE RADS . RISERS AND MAIN PIPED TO SPEC. THE APPROX 60FT MAIN THAT RUNS STRAIGHT ALLONG FRONT OF HOUSE HEATS GREAT.THE MAIN IN THE BACK OF HOUSE WITH ABOUT 10 90'S AND ABOUT 90-100 FT HEATS ONLY ABOUT HALF WAY. NEW MAIN LINE VENTS  AT THE END.ALL PIPE INSULATED. ALSO WE HAVE A VALVE IN THE SHORTER MAIN TO SLOW DOWN THAT SIDE. HOMEOWNER TELLS US THE OLD BOILER ALWAYS HEATED ALL RADS. PLEASE HELP !                                                                                                                                                                                                                                                      

Steamhead

What pipe sizes

are your mains?



What vents are on them?

Volvoguy87

Cold Main.

Test the vent on the cold main and see if it's good or bad. 

Could something have fallen down a riser and blocked the cold main?

Is there a dip in the cold main filled with water?

Is this a one pipe system or a two pipe?



Could it be that the cold main is fine, but the vent on the hot one isn't?  By which I mean, is the vent on the functioning main too fast relative to the one on the cold main?



I'm only a novice, but I hope it's of some help.

Dave