test results from a Laars Endurance

snugone

I have a condo with an older Laars Endurance EBP running off natural gas that was installed around 2002. Although its had an assortment of repairs over the years, I am not aware of it ever having been tested and calibrated.

Over the last year or two it has been starting with a noticeable pop noise (or 'whoomp') when the flame ignites but otherwise seems to be running fine. So the other day I performed a combustion test just to see what the numbers were, using tools I had for my oil fired boiler. (I'm comfortable working on oil, but gas is still very new to me.)

stack 252.5F
ea 33%
co2 8.6%
o2 5.7%
eff 84%

I should mention that the combustion test was performed in normal fire mode, and not the forced high fire mode it should have been performed in. This unit requires shorting jumpers and at the time I was without internet access at the location and I wasn't going to do that without being absolutely sure I had the correct pins. I will jumper it properly on my next visit and re-perform the test. Might not matter though, as the unit stays in high fire mode for a long time at the beginning of its cycle and that is the period during which I took the readings.

The manual says co2 should be between 9.0% and 9.6%, so that 8.6% is a bit off.

I also took gas pressure readings from the outlet pressure port on the gas valve and got -0.23 inches w.c. For the heck of it I have posted video of the pressure readings during the pre-purge and ignition periods.

https://www.youtube.com/watch?v=lFXyHgIVY1I

The manual appears to say that during the pre-purge that the outlet pressure should drop to several negative inches w.c. and that does seem to be happening. It says it should then settle back to between -0.01 and -0.10. So the -0.23 I'm measuring seems very off.

All I've done so far is take measurements. The condo unit is a couple hours drive away so I probably won't be back there for a few weeks. Time enough to get a plan of attack together I suppose.

To raise the co2 up into the desired range I could try closing the adjustable air inlet some, but I would think that would in turn cause the gas valve outlet pressure to go further in the wrong direction. I could adjust the outlet pressure at the gas valve, however I wonder if there's some clues here that might indicate that the gas valve is on its way out and that it's not worth fiddling with.

I do happen to have available to me a new-in-box Laars supplied gas valve for this unit that I could swap in and then all that would be left would be to adjust the adjustable air inlet to get into the proper co2 range, assuming it doesn't return to that range with the new gas valve alone.

Thoughts?

Tim McElwain

Which valve does this have on it make and model, that will help to determine adjustment if any?

snugone

Tim McElwain said:

Which valve does this have on it make and model, that will help to determine adjustment if any?

It's Laars part 2400-548, manufactured by Honeywell. I don't know if it helps, but here's a catalog picture with a closeup of the valve's side label.

EDIT: I believe it's a Honeywell vk8115v 1069

Tim McElwain

The VK8115 is a European Honeywell negative pressure gas valve.

Adjust as follows at maximum firing rate:

The outlet pressure should be between -.01 to -.10 I have found that at about -.08 it is good.

When adjusting the offset pressure the CO2 will reduce as the offset pressure is adjusted more negative.

If CO2 is still less than 9.0 then close off the adjustable inlet.

To get on high fire press the enter button and the up arrow on the boiler control and hold for 2 seconds you will then have high fire for 5 minutes.

You are looking for 9 to 9.5% CO2 with O2 at 4.5 to 5%.

Tim McElwain

By the way what was your CO air free reading?

snugone

Thanks. I'll make those adjustments when I'm next on site, which could be in 2 or 3 weeks. I'll update this thread after that with the outcome.

Tim McElwain said:

To get on high fire press the enter button and the up arrow on the boiler control and hold for 2 seconds you will then have high fire for 5 minutes.

This particular unit is the old model, before Laars added in all those fancy features. To force high fire on this one, the control board cover must be removed and a pair of pins on the circuit board shorted out.

By the way what was your CO air free reading?

The meter I possess is a SOX3 which isn't capable of CO measurements, so I'll be calling in someone to measure the CO levels following my work. Though it would be interesting to know what they are right now of course. At least the CO alarm not far from the unit has never registered anything, but all that really means is that the unit is venting properly.

snugone

Had chance to visit the condo earlier this weekend and tend to the boiler while there.

Forced high-fire mode and adjusted the gas outlet pressure to -0.08. Was worried that it having been so far off might be a symptom of a valve on its way out, but the -0.08 held consistently steady.

After that, needed to close the air inlet very slightly to attain a measurement within the wanted co2 range.

Here are the new values, taken while still on forced high-fire mode:

stack 304.2F
ea 26%
co2 9.1%
o2 4.7%
eff 82%

The efficiency went down slightly, presumably due to the higher stack temp, but I think the numbers that matter most are now within their correct ranges which I guess indicates that it's a good clean burn. Sorry, no CO reading to report yet.

I have a newb question about gas valves, or at least this particular design of valve. Are they expected to gradually stray from their initial settings as they age and require periodic adjustment to account for that? If so, I would then assume that at some point they stray so much that further adjustment is impossible and replacement is necessary.