Question about tekmar boiler controls....Boilerpro

Boilerpro_3

at a customers home with a 260 control set for auto differential and full reset. Control settings are very tight, so system flow is nearly constant. Single zone baseboard hot water with indirect domestic, 190F design supply @ -4F outdoor, 70F indoor design. Burnham 2B boiler 198,000 input with NRF-33 pump and 140F Esbe mix valve on boiler return piped P/S to system. At the time, outdoor temp was 47F and supply was running from 120F to 130F between boiler cycles. I noticed some condensate corrosion on the B vent and it seems to me the boiler was running pretty short cycles (only a couple minutes firing time). Is this operation normal? I would think that the auto differential would open up the differential in warmer weather to create a longer burn time and was wondering how this could be done other than going to a set differential.


Boilerpro

Unknown

Dave

Put together a little sketch and post it if possible of how this boiler is piped into the system. What is controlling the mixing valve or is it just set to divert? What are the control settings relative to boiler target and minimum boiler temperatures? What type of radiation is the control set for. I'd like to see this corrected before things get too bad. Let me know and I'll be glad to advise. Hope this helps.

Glenn Stanton

Burnham Hydronics

Boilerpro_3

Hi ya, Glenn...

The problem appears to be a control problem, not your boiler, but just the same I'll try to fill in the blanks. Mixing valve is thermostatic controlled for 140F minimum return to boiler(Esbe thermix valve). Boiler with mixing valve on return piped Primary/secondary to system. No minimum supply temp since mixing valve is protecting boiler. Control set for baseboard hot water. System target at time of viewing was 125F (middle of 120 to 130 differential). Boiler running about 150 on guage. I believe the condensate is forming because the on cycles are too short, not allowing enough time for the vent to heat up. I believe the control is supposed to operate the boiler at a larger differential during light loads to ensure longer burn times and prevent this problem. Sorry for no sketch. Have no scanner right now and just learning how to use my digital camera. I'm hoping to get someone from tekmar on this...I plan on calling them next week. Thanks again for you prompt response, as always!


Boilerpro

eleft_4

260

try this it's d, there is also a, could be set man. or auto

al

Unknown

Dave

I realize all too well that it may be a system control problem, but I feel that it could also be a system piping problem which may soon become a boiler problem. If you are condensing in the flue, then you are also more than likely condensing in the boiler flue passageways. If the boiler gauge is indicating 150°F, then the return water has to be somewhat cooler or about 130°F. Is this a thermostatically actuated valve or simply a diverter valve? Is this valve on the primary loop where the boiler return branches off or is it set up to control a system bypass by blending hot boiler water with the cooler system return water? Is the differential option on the control set for automatic or manual and finally, is this set up for boiler injection into the primary loop?

Glenn

Thomas Mörtberg

Hi!
I think that when the heating load is small the firing boiler has no problem increasing the supply temperature.
Setting the Tekmar to manual differential will extend the runtime but will also cause a lower average supply temperature during design load. The amount of water in the secondary piping might be to small for the amount of boiler water. Does the water temperature drop as quick as it rises?
The thermostatic valve may or may not work, the short runtime is not helping there.

Boilerpro_3

Glenn and others, stopped by that install today

The water appears to be coming from between the inner and outer layers of the B-vent. They still need to do some repairs on the masonry of the chimney, so water may be leaking in from there. I checked the inside of the B-vent and it was as clean as new (no white powder). Also took a look at the burner tray, and short of a few burnt insects, it is spotless.... no rust whatsoever. Boiler temp guage shows 142F while firing (but we all know how inaccurate most new guages are). The Esbe Thermix valve is on the boiler primary piping (boiler loop) right as the piping goes into the return of the boiler with the boiler pump on the boiler supply. After the pump on the boiler supply, the supply splits with one line going to the mixing valve and the other out to the primary seconday tees on the secondary (system) loop. The boiler pump injects boiler water into the pimary loop and the quantity of water injected is effected by the thermic valve on the boiler return. I talked the folks at tekmar, and the minimum on time for the boiler in the software is 30 seconds.... much too short in my opinion. I reset the differential from auto to 20 degrees to increase the firing length. The system temp changes gradually during firing and does not drop quickly after the flame shuts off.... indicating there is plenty of flow through the system. The boiler pump is cycled with the system pump to prevent short cycles due to the stored heat in the boiler spiking the supply temp if it was cycled with the burner. However, for all pratical purposes both of these pumps run continuously because the heating curve is set very tight to the heat loss curve. Thnaks for your help!


Boilerpro