[ATTACH]44778[/ATTACH] There is a small leak, seemingly caused by a torn o-ring on the PEX connector (blue arrow), connecting pipe to Wirsbo manifold (see attachment). I can't seem to determine the size of the o-ring and a trip to the shop didn't help. Would someone please tell me what size o-ring is required?

Sorry everyone. I wasn't sure where to put this. My boiler is working great and one thing I do to keep warm air in the house is put a cut-to-size piece of foil insulation in my air return of my central air and I tape 11 x 11 sheets of aluminum onto my ceiling registers. Even closed, I still cover them. My thought is to keep the warm air in the house and not seeping into the attic through the air return and registers. I never see anything about this anywhere but I do it. Two things: when my boiler comes on in the basement, I am up on the second floor of the house and I can hear it come on (bedroom side of the house next to the chimney) and I also see the sheet of aluminum drawn up for a second. When anyone comes in through the front door or the side garage door leading to the garage, any and every aluminum sheet gets drawn up/pushed up for a second. This tells me a house really is pressurized and when there is a draw of air for the boiler or a change of air pressure because a door opens...warm air really does get sucked out of the house. This also reminds me air leaks are always important to deal with and based on the movement of the second floor aluminum sheets covering the registers when a door opens (even when the bedroom door is closed) to the outside, there really is a loss of air through central air registers, even when slid shut. The basement is insulated, there is a poured slab wall, and just a wall on the heater room side is not. The boiler does not soot up and at the annual cleaning it looks good inside. I am just surprised that there can be such air movement with the central air registers closed, and covered, when a bedroom door is closed and a first floor door opens. I "see" it with the sheet of aluminum moving. My thought is if we all have central air, we are losing a lot of heat if we do not cover the air return and ceiling air registers for the winter. I do this around Thanksgiving until second week of April. Anyone have any thoughts about this? Am I wrong about air pressure in the house and loss of heat up the air conditioning system?