Vaillant floor gas boiler, combustion gas smell

Keith Perkins

I have a 12 year old 83% effecient Vaillant floor gas boiler in my garage feeding 3 seperate hot water heat zones. Its a 1 pipe system. It has a draft hood and an automatic vent that opens before the boiler fires.
Most of the piping is black iron with copper feeds to the radiators. The expansion tank is in the attic above. It heats well but there are several problems.

1. One of the zones makes a buzzing sound when its on (low level hum heard everywhere there is a radiator)
2. In another newer ( ~ 5 years old )zone I can hear water running in the pipes when its on.
3. The garage is always very warm and my gas bills are very high.
4. The boiler leaves a burned gas smell in the garage. (The CO alarm has never gone off. I resealed the vent pipe and this partially fixed the problem. I am going to redo the flue after this season and take 2 turns out).

I had it serviced the last 2 seasons ( including bleeding the system of air) and cleaning the boiler box. The technicians were unable to solve any of the above problems. Any recomendations for how to solve them. Any contractor reccomendations for Newport News VA?

TIA
Keith