Let me preface this by saying that my current system is only heating a small (approx 1000s.f.), single story , stucco walled, slab-floored, 1950 home in the SF Bay Area (with generally mild winters, it is very rare that we ever reach freezing temperatures). The original American Standard boiler is still in place, and until about 3 years ago it used the original B&G pump (now using a Grundfos 15-58). I have no way of knowing the exact layout, but the pipes are copper, embedded in the concrete slab. I have lived in this house since 1992, so I have a pretty good “history” of using this system: it initially took a few years to get used to the unique heating characteristics of this “high thermal mass” setup. At first, I just left the boiler alone, and it was clearly set to run fairly high temperatures for a system of this type, as I constantly had problems of overshooting the target temperature – subsequently the system would not have to run at all for the next 18-24+ hours, then a repeat of the overshoot. Once I learned a bit more, I have learned to adapt: the water temperature is run lower, and I now use a programmable thermostat setup in the opposite way from most people: it is set to “bump-up” the temperature a couple of degrees during the roughly 2AM to 8AM period, then set back to a slightly lower temperature during the day. This works surprisingly well for our climate here, but I’d like to see what I can do to improve efficiency. Now for the shocker to all of the experts here: the system uses a gas water-heater style control valve mounted to the point where there would normally be the aquastat. Yes, this uses a standing pilot setup, just like a water heater, and the only high/low cutoff device is this gas control that literally is of the same type used on water heaters. The thermostat is wired to a simple switching relay (Honeywell RA889A) that directly starts the circulator pump every time there is a call for heat. Obviously, when first started up, there is a significant temperature drop (Delta T) when the hot water starts running through this cold concrete slab, but naturally this gradually lowers as the system runs for a period of time. I have the possibility of adapting this to a more conventional aquastat and electronic ignition/intermittent pilot (Honeywell S8610U and VR8304M) at no cost to me (a next door neighbor had their complete boiler swapped out for a newer mod-con style a year ago - $13,000!!- I grabbed the old boiler and saved the installer from have to haul away this 200lb. beast). What this would also allow me to do would be to update to an outdoor reset control –something along the lines of a Tekmar 256. This would allow the system to essentially completely shut down during the generally mild daytime conditions we experience here, as well as run in a more effective manner when called for ( it has some ability to adapt the water temperature to demand level). Would anyone care to comment on the validity of my proposed solution, or, better still, care to guess what kind of gain in efficiency I might achieve?

I don't know what the pressure was before I replaced a leaky valve, but the system was working at the time, minus 2 cold baseboards. Now that a lot of air entered the system while replacing that valve the system pressure is at about 5 psi. The temp goes from about 170 where the boiler turns on, to about 220 or so. I tried bleeding the air at the baseboards, but when I open the bleed ports, air actually is being sucked into the system! :( Help please ...