CGi-3 short cycle, low temps

Jimbo_5

I am dealing with a Weil Mc CGi-3 that fires for about 10 mins, supply barely reaches 120°, then shuts down having satisfied the t-stat. It's in a 2-story duplex with firewall separating the two, each with own heating system, each side is apx 460 sq ft per floor for a total of 920 sq ft heated space, fintube along entire outside walls, single zone for both floors, stainless exhaust running about 15' to exit outside wall in unheated basement. Boiler is set for 180° and installed in 2005, with a kit (381 354 595) installed the end of 2008, it has 2 drain tees on the exhaust attached to a condensate pump. It is presently 28° outside she just fired for 10 mins with supply getting to 120° and return 100°. Granted the sun is out and my south-facing walls/windows are radiating heat, but this sure seems unusual to me. Any ideas. Didn't fire again for 35 minutes, and then the same numbers, just below 120°, returning 107° stasfied in 10 mins, 29° OAT, no sun on house now. Funny, she just ran a quick air purge 4 mins after shutting down, lasting only seconds.

Jimbo_5

It's almost funny, because the house was built in 1890 at the Jersey shore. I called Weil McLain this morning and their tech really didn't know what to respond, saying "it's lasted 10 years without noticeable damage, so it must be all right." He figures the tees draining into the pump catch the condensate. It's awfully weird to me.

Jimbo_5

OK, now I am beginning to question the t-stat. Although the digital temp reading has not changed on the t-stat it fires up for that 10 minutes. Could it be that the t-stst does not "allow" the temp to drop enough before calling for heat, thus causing a very short run time? If I raise the called-for temp by 5° she fires and reaches 180° supply and 168° return. The induction fan gets above 200° too.

Gordy

Its possible the swing on the tstat is tight. But then there goes the comfort if you widen the swing.

FranklinD

Take heart, you're not alone. That's exactly the way my boiler runs as well. At 0* outside I have a supply water temp of about 125*-130*. I have cast iron radiators, though.

Jimbo_5

It does seem as though the t-stat is saying "enough" too guickly, or it is calling for more heat when there is only 1° or so before hiting set point and shutting down. There must be something I can do to fix this condition.

Gordy

How is the boiler piped? Bypass, Primary/secondary, direct?

Gordy

So is your concern the cycling??

Jimbo_5

Direct.

icesailor

What kind of thermostat? Electronic or old fashioned analog like a T787F Honeywell? You usually raise the heat anticipator higher. Or, higher than the heaviest amp draw of any control run through the thermostat.

Electronics, chance the cycles per hour setting.

Jimbo_5

I have a Honeywell electronic. Fancy programable, but totally unneeded. And I think you hit the nail right on the head, because it seems to fire-up every hour, needed or not. But how to alter this thing will be a challenge.

FranklinD

I've played with the cycles per hour on my Honeywell...I've finally settled on 2 CPH. The old monster boiler always ran best at 3, but this new boiler is 2/3 the size.

If I have mine set at 66, the boiler may cycle on at the the low end off 66 and run to 67, or it may not cycle on until it actually drops to 65, then run to (what I assume is) the upper end of 66.

The low water temp is just a byproduct of having more radiation than needed to heat the house at a given water temp.

For example: say you removed half the baseboard in the house, I bet you'd be running a 170-180* water temp to maintain temp. But since you have wall to wall baseboard, you just don't need water that hot to satisfy the thermostat. That's the type of situation that a mod/con boiler is made for.

Since it's direct-piped, is there a boiler or system bypass (a cross connection between the supply and return pipes, with a valve in it, at the boiler)? I know the WM manuals spec them for low return temp situations...but 'usually' not needed for baseboard installations.

Jimbo_5

No, no bypass installed. If it would truly help, I would cut one in.

Gordy

All the swing does is hold a tighter range for set point. The tighter the range more cycles per hour. The wider the range the less cycles, but the more deviation from set point then occurs.

Jimbo_5

I can easily stand a greater deviation from the setpoint, that's not a problem. But I'll have to figure out how to change this t-stat.

Jimbo_5

The t-stat is a Honeywell T8112D but I cannot bring up the manual on line for some reason.