Low water cut-off adjustments with Tekmar 279 Steam Controller

cubicacres

We noticed our low-water cut-off seems to be shutting down the boiler during the heating period of the heat cycle on occasion as it then lights up with a delay before refilling (but the condensate returns in about 5 minutes after shut-down rather than use the feeder with its 10 minute delay). We have been using about 5 gallons this past month, so sometimes it must be feeding new water or we have a hidden leak somewhere. Funny the Hydrolevel brochure mentions up to 15 gal/month as normal for our boiler size, since we thought 1-2 gal/month was better.

Other times the water feeder light doesn't appear, so maybe the Tekmar has finished its on-time of the heat cycle? Tekmar tech support reccomended increasing the lockout differential to allow the condensate to return on its own to allow for a full heat cycle next time without running out of water, which makes sense.

Has anyone else had this issue of interrupted heating due to low-water with a Tekmar boiler controller? We suspect this interrupts the Tekmar's timing of the heat cycle, as it appears to keep on running through the heat cycle time of 40 minutes we have it set for currently. Any reccomendations to maximize the amount of condensate return to the boiler so we can minimize our new water intake during the heating season and avoid it shutting off on low water as much as possible?

Once the Low-water cut-off shut off with no visible water left at all in the gauge glass, but usually it shuts off with about 3/4 inch at the bottom and the feeder button begins to glow-this was interesting to us last week when we first saw it. Maybe a seperate issue?

Fred

Have you been properly skimming that boiler? It sounds like the water is being pushed back into the returns. When the boiler is idle, is it over-filled? That much water is way, way to much water loss. It has to be going somewhere, if the boiler doesn't over-fill. What size is that boiler? I have a 866 Sq. ft. of steam and the only water I have to replace is about a quart when I remove a quart or so with a blow-down. The amount of water loss printed in the owner's manual is absurd.

Bio

cubicacres said:

Once the Low-water cut-off shut off with no visible water left at all in the gauge glass, but usually it shuts off with about 3/4 inch at the bottom and the feeder button begins to glow-this was interesting to us last week when we first saw it. Maybe a seperate issue?

It doesn't shut down because of the foaming going on around the lwco probe, which means there's still some more oil left inside the boiler (removing 100% of the oils is a long process), this also makes wet steam which carries some water out of the boiler to the system, more skimming or tsp cleaning is needed, boiler should shut down just past the probe

cubicacres

We did a brief cold skim for about 30 minutes at the beginning of the season until the cruddier water on the top ran clear for a while. We could do more and use the pipe test to remove more oil, but just tried a quick skim using the appearance of the water as a guide.

We didn't see another leak yet. The low-water cut-off & subsequent refilling of the boiler is from condensate to refill the boiler sometimes, and uses the water feeder other times from our observations. If we up the lockout differential, we hope to let as much condensate as possible return so the water feeder doesn't have to run very often. Tekmar advised lengthining the lockout differetial and keep increasing it until the condensate returns and refills the gauge glass back to the full line or about halfway up the glass. The gauge glass is filled with brown crud, which makes it difficult to see the water level when it less than 50%, so we'd like to clean it. Does that new crud in the gauge glass suggest it needs more skimming?

JohnNY

As suggested above, this is not a control issue. This is a general system fitness issue. It sounds like your boiler water needs a better skimming and all around cleaning, but I'm wondering about the condition of your return piping as well. If it's original, goes under the floor surface at some point, or looks like it was reduced in size (diameter), then I'd be suspicious and look deeper at that situation.

cubicacres

We had a 30 minute cycle time, then increased it to 40 minutes. I think the boiler % run time was around 28%, but has been changing as we change the tekmar settings. About 4 hours per day run time if memory serves me correctly with mid-20s the last few weeks outside.

Foam keeping the probe satisfied makes sense. Our visible sight glass seems empty (but lots of brown crud), so that was worrying us we could risk dry firing or something.

For anther skimming session during the heating season, would waiting for a warmer day be better to let the oil solidify at the top? Then do another cold skim, feeding water & run the boiler for 20 minutes to dissolve the oxygen? We don't have a homemade copper water wand to do a more thorough job & just ran it until the water cleared up last time. Is Dan's pipe test method the next best way to go to see how much oil is left then?

As an aside, we noticed our short main vent is too hot to hold after 5 minutes from boiler ignition (almost 1 minute for the entire ignition sequence to complete in our WMC EG-75), a minute later the middle loop vents are too hot to hold, and the long vents follow 4 minutes after that, with the last radiator in the hallway on the long loop too hot to hold 3 minutes after the long vents get hot. 5+1+4+3=13 minutes until all radiators are getting steam & too hot to touch their supply pipes at the floor level per our observations. Does this seem reasonable for a 5 unit building on a 20-30F day in Milwaukee?

cubicacres

Does the longer 60-90 minute cycle time allow an inside & outdoor sensors (we have one each) to learn how long to run to satisfy the indoor desired temperature over time?

Interesting the steam established was set at 160F last year, we used 15% more gas than the old larger EGH85 boiler with no tekmar or WWSD devices, then we felt the last radiator & set the steam established to 130F last month when it got too hot to touch, and now we're using 15% less gas than the old boiler this past month. Does a 30 degree lower steam established setting use 30% less natural gas over a month? If other have noticed this, this may be what we were supposed to be dialing into for the tekmar gas savings.

Our condensate returns about 5 minutes after the boiler stops (on L low-water cut off or the tekmar) when the condensate sensor reads about 120-123 or so. Does this suggest a small lockout differential or should be make it larger to allow more time for condensate to return? It seems the lockout differential is using temperature to measure time for the condensate to return to the boiler since anything under 212F should return as condensate (hot or cooler water).

cubicacres

Our boiler was still using about 1 gallon a day instead of per month (has been for a few weeks & no leaks in the basement mains found), so we did a skimming for an hour or two yesterday, and noticed a few things:
1. We shut off the boiler for 40-50 minutes, then saw the internal temp. was around 180F with an IR laser thermometer, and fed 29 gallons of water manually from our VXT-24 water feeder. We were a little nervous about the street water temp. differential, but the skimmed water in our 5 gal buckets dropped from 180F to 120F or so in about 90 minutes of skimming.
2. The first 2 water samples we took from the boiler we boiled in a pyrex flask had 20 degree lower boiling temperatures than our tap water sample, then after 29 gallons were skimmed out, the 3rd sample boiled at the same temp. as the tap water and didn't look as foamy as the first 2 samples did-similar to the tap regarding foaminess.
3. We thought we saw oil on the surface of the water leaving the boiler from the skim tapping before it dropped in our bucket when we shined out flashlight on the water, but wondered if it was just steam on the water's surface since there was steam coming out with the water in the first 30-40 minutes. It stopped appearing after 60 minutes of skimming, but the temp. also dropped to 120F over time as well, so we're not sure if it was oil leaving the boiler, or just steam when it was hotter water.

Any thoughts on our observations? We forgot to clean the LWC probe & gauge glass this time & didn't want to risk breaking the glass since our last contractors did. We'll ask the tennants to look in their apartments since that gallon per day the past few weeks must have been going somewhere. Any guesses on where leaks appear more commonly? Or was it just make-up water with a surging, dirty boiler that needed more skimming?