Swap vaporstat for pressuretrol

Rightrudder

I have a Honeywell pressuretrol 404A that has gone a little wacky. I’ve got the cut-in bottomed out to the bottom of the scale, and the cut-out bottomed out at 1.
I have two gauges, teed off from the boiler, each with its own pigtail, and the pressuretrol is teed off of one of those. They both read accurately +/- less than1/4 psi.
The boiler cuts out at 2 pounds, and the pressure drops all the way to zero, after which point the boiler sits for a minute or two and then fires back up, and the process continues. On occasion, the lag has been long enough that the main vent vacuum breaker opens. I’ve been considering swapping out for a new 404A, but I’ve read a lot about the benefits of a vaporstat. I’m comfortable enough working around the boiler that I think I might be able to swap one out, but not sure what model would be a good replacement, or any fine-tuning that I would have to do. Thanks for your attention!

Rightrudder

By the way, I forgot to say that if I belueve the problem is with the cut out. If I bring the cut ends in up to .5, the boiler doesn’t cut out until closer to 3 psi. Thanks.

nicholas bonham-carter

Pressuretrol are notoriously inaccurate, so a vaporstat (0-4 psi), would be more accurate, and you should have a more accurate low pressure gauge, capable of measuring ounces of pressure, (0-3 psi).
Your boiler may be oversized, or lacking in main venting capacity, but you won’t know that without an accurate gauge.—NBC

Rightrudder

Thank you, NBC. Actually, I have 2 5-pound gauges that both really pretty similarly. This is a relatively new problem, and I haven’t had any changes to the system or vent valves.
For years, I have had a cut in at .5, cut out at 2. So, with this new problem, I think the pressuretrol has gone a little bonkers.
I have no problem changing out my pair of 5’s for a pair of 3 pound gauges, But any idea what make and model vaporstat would be an appropriate replacement for the current Honeywell 404A?
Thanks!

Jamie Hall

L408J1017 0 to 4 psi.

Fred

Or recalibrate the Pressuretrol:
If you see the pressure on the low pressure gauge go much over 1.5 to 2 lbs follow this procedure to re-calibrate the Pressuretrol:
Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn too much, a tiny fraction of a turn goes a long way towards getting it adjusted where you want it (maybe 1/32 inch turn to start with) . You may need to play with it to get it exactly where you want cut out to be.
If you have difficulty turning the tiny set screw because of the Lock-Tite, use a small soldering iron to melt the Lock-Tite.

JUGHNE

Also, if you try to bottom out the adjustments too low the mechanism falls apart. Have you checked that first?

Rightrudder

Yes, I cranked it until I was just shy of the thing falling apart, but I’m confident that the spring and attendant parts are all intact. Thank you for checking.

As for recalibration, that is intriguing. I wasn’t aware that that was doable, and I will try it. I am pretty sure that the cut-in settings are OK, it’s just the cut-out that has become the beast.

And if all this doesn’t work, and I will probably give that model vaporstat a try.

Thanks to all! This is such a great forum!

JUGHNE

Did you mention that you are sure the pigtail is clean?

Fred

@Rightrudder , that procedure is to re- calibrate the Cut-Out.

Rightrudder

Yes, 2 new pigtails (one for each gauge) are clean and both gauges are in sync +/- <1/4 psi. Thanks again for checking.

Yes, the cut-out is what I am trying to rein in. Looking forward to breaking out the hex key tonight!

B_Sloane

you did not mention the Structure that this is installed in ..
2# is a hello-a-lot of Steam !!

Rightrudder

It’s just a single family, 2 1/2 story house. Single pipe steam, Utica boiler rated 375 ft.² /90,000 btu/hr
I had read long ago in a steam heating book (this is before I had the great fortune to discover Dan and his amazing resources, of which I own several) that the 2# out/ 1/2# in was a good target to aim for a smaller structure. So I have stuck with that for all these years. I figure that the lower cut-out would cause the boiler to cycle too often. I have seen 1-1/2#
cited in some posts on occasion, but unsure of their particular situation. I’ve stayed with the current formula because… I guess that’s just what I’ve been doing. Can I be doing better?

JUGHNE

How is your steam main air venting?
Have you calculated your connected EDR?

Fred

@Rightrudder , 2 PSI is the top end of where you want the pressure to be. 1.5 is better. Many of us run in the ounces. The lower the pressure, the faster steam moves through the system. How often the boiler cycles will depend on how over-sized it is compared to the connected EDR (radiators). If you use a set back on your thermostat, that too will cause the boiler to run a longer cycle and, if the boiler is over-sized, may increase the number of cut-outs. We typically recommend no temp set-backs or if you, not more than a couple degrees.
My boiler is over sized and I run my vaporstat at 4 ounces Cut-In and 12 ounces Cut-Out and I never get any short cycles except when the outside temps dip down to 0 or below and even then I may only have one, max two burner shut downs on pressure but I set my Thermostat at the temp I want and never use a setback.
Having really good Main venting is essential! It keeps your system from building pressure before the steam is on its way to the radiators.