Tekmar 256

Damon

With a Tekmar 256, non-condensing gas CI boiler on a 2 floor converted gravity system with CI rads is it best to wire such that the 256 always maintains the target temp while allowing the zone valves only to turn on the system pump with the 256 having no connection to the pump or should the 256 and the zone valaves both operate the pump? In other words is there a problem with firing a boiler without the pump running or is it better to always have flow through the boiler anytime the boiler is fired? The flow would be through the bypass if the zone valves are closed. Also, besides primary/secondary what would be the preferred bypass type with such a setup (system or boiler) and why?

Unknown

Damon

You will likely find any converted gravity system w/ci rads always works best when it`s constantly circulated within that zone. The boiler and boiler-pump will add heated water(to what the 256 says) to that zone when the stat tells it to.
If I understand your question correctly.

Damon

Tekmar 256

Thanks for the quick response Dave! I'm only working on a partial reset so I don't want to circulate water through the zones continuously since I will overheat this time of year. Is it OK to fire the boiler with no circulation at all just to keep the boiler at the 140F target or would it be better to a) fire the boiler and just circulate through the bypass to maintain target or b) fire the boiler only when the zones call for heat? Thanks!

Mike T., Swampeast MO

Unless it's an older (say 60s or before) boiler with high water content, I would not fire unless a zone circulator is running. If you fire to keep just the loop around the boiler hot with a more modern low water content boiler you'll get short-cycling and excessive standby loss.

Realize however that in moderate weather you're unlikely to ever achieve 140°F target unless your bypass valve is a thermostatic version similar to ESBE thermic type TV.

Fortunately, atmospheric cast iron boilers driving gravity conversion systems don't seem to have a problem with condensation even when operating at quite low temperatures. I've asked here numerous times over many years for photos (and even stories) of such, and nobody has replied.

Damon

Mike

It's a less than 1 weeek old Peerless MI-05 which holds 7.28 gallons. Short-cycling and excessive standby loss is what I'm seeing/concerned about since the way it was wired the Tekmar and the zones both fire the boiler and run the pump. It has a system bypass and it does trip the aquastat high limit because the tekmar holds the 140 target then the zones call for heat. They are coming to do a complete rewire tommorow. If you want to see what my 21 year old Utica M150AGB looked like after a good cleaning and the effects of 2 weeks of condensation check this thread:

http://forums.invision.net/Thread.cfm?CFApp=2l.&Thread_ID=39934&mc=1

I sent the pics to Utica who thought it was probably condensation or possibly pinhole leaks that only opened up temporarily during cold startup since there was no pressure loss or makeup.

Mike T., Swampeast MO

Interesting. Can you perhaps edit the post with the big picture of the HX so you have to click to see? (Remove the display with message checkmark.) Really hard to read the message itself when you have to keep scrolling.

Old boiler and flue looked cosmetically perfect. From all I've seen and been told, condensation problem [usually] appear first in the flue piping.

I could well be wrong, but the discoloration at the bottom of the HX looks like there has been excessive heat. Perhaps because it was configured to fire without a circulator running?

Am also curious about your zones. You say two. You have cast iron rads and fin tube in the basement. Are these perhaps your zones? You've seen the heat loss so you know the basement needs little heat--if the basement is its own zone capable of firing the boiler it's going to produce WAY more heat than needed (and able to be liberated).

Damon

Unless I'm doing something wrong, for some reason the older post is not giving me the edit option but today's posts do. You should have seen it before I cleaned it (sorry no pics): ~40% plugged with some where between 11-21yrs of rust, ash, soot, scale and 3 broken studs. The galv. flue pipe was prety corroded with large flakes but not rusted through. The flue collector was badly corroded and in need of replacement. The pump always ran when the boiler fired. I'm pretty sure the black discoloration is water marking from long term leakage and/or condensation with the corrosion on the bottom of the second pic with the link being from condensation. Just my engineering opinion. I have 1 CI rad zone for 1st and 2nd fls and one 40 ft copper fin tube zone in the basement. The 40 ft matches the heat loss (83 yr old house) which yes is a small zone. We rarely use the basement but want heat down there when we want to hang out down there and watch the big screen or entertain.

Mike T., Swampeast MO

Sorry. That was Steamhead's photo I saw, not yours... Sure thought it looked pristine.

Mike T., Swampeast MO

Of course I can't see how the old boiler was piped and controlled, but here's an idea of how that system could have had a severe problem with condensation and/or thermal shock.

Say the basement baseboard zone calls by itself. The boiler heats RAPIDLY to aquastat setting and cycles at high limit until the call ends. If the rest of the house calls for heat at the same time, a HUGE amount of relatively cool water floods into that nice, hot boiler. Can't be pretty...

I'd verify with the installer that he thought of this and took measures to prevent it from happening. If not, your new boiler could well suffer the same fate as the old.