Pressuretrol settings. Cut in @ 3 lbs. Diff @ 2 lbs. Thoughts ?

Respectfully, Coach (and I love that username by the way, Bad News Bears reference), you keep asking "why would someone do this" for things that are wrong. People do wrong things, let it go.

OK the reason people often did that was to lessen "short cycling" which they saw as undesirable. But what it causes is needless fuel burning to raise the pressure way way higher than it needs to be.

Try 1 cut-in and 1 diff

Eek. That pressure setting will trash your vents… try setting both scales to 1. However, that unit is old enough that it may not be all that accurate, so it might not be a bad idea to install a good low pressure gauge on the system — you can do it on the same pigtail with a T, a couple (maybe 4) close nipples, and two 90 elbows.

Do you have a low-pressure gauge on Cedric, @Jamie Hall ? Or is that just what the vaporstat is set to? I would bet the whole house gets plenty of steam at way less than 4 ounces.

Based on what we see around here, they are compensating for a complete lack of knowledge on getting the system to perform properly.

As an aside, it is a safety device, with a properly operating system, and a properly sized boiler it should essentially never activate. The boiler should just heat the house and you are good.

If it's working correctly, and you are hitting that limit at all, you can be fairly certain that boiler is massively oversized.

Pressure would hit limit too early because why? How does oversized boiler play into this? Explain like I am 5.

The boiler makes a fixed amount of steam every given time period, depending on its size rating. Steam has about 1700 times the volume of water so the steam starts to create pressure in the boiler.

The pipes carry the steam to the radiators (pushing the air out as it goes), where heat is…radiated…causing the steam to lose its latent energy and return to liquid state, and return to 1/1700 the volume it had before.

So if the radiation in the house (all the radiators) can't condense steam fast enough, pressure will build in the system.

This pressure is unnecessary, and can become dangerous, so there are a couple safeties on the boiler to prevent this pressure buildup.

One is your pressuretrol, which "cuts out" the boiler (shuts it off) when the pressure gets to your "cut in" setting plus your "differential" setting. 1 psi is way more than enough pressure for steam to move through the system (about 1/27th that is all that is needed, but it's hard to create a safety device that is this accurate cheaply, so we get Pressuretrols which only activate around 2 psi).

My thinking is there is no reason in the world to be burning fuel when the system gets into this state of "too much steam", so in my system, if I get up to about 2 ounces per sq inch, then my boiler shuts down for about 10 minutes to let the radiators send their heat into my rooms.

The pressuretrol is simpler than this, and it will let the boiler run again when the pressure gets down to about the "cut in" point.

The important thing to know is the pressuretrol does not "set" the pressure in the system, it simply acts as a pressure limit for the system. As @KC_Jones said, a well-sized system doesn't hit this limit very often, but well-sized systems are rare.

if it's oil, an oil technician might be able to down-fire it.

If it's a gas atmospheric, you can lower the gas pressure a little, otherwise just let it cycle.

Hello CoachBoilermaker,

Personally I think the answer is quite simple. Once the system is at the point where the pressure is rising significantly the radiators can't condense the steam at the same rate as the boiler is producing it. Pipes are hot and the radiators are hot. So shut off the boiler (Pressuretrol, Vaporstat or your favorite low pressure switch) then the pressure will drop quickly, and once the differential of the pressure switch is satisfied the boiler will restart, and the short cycling will begin until the thermostat is satisfied. On-Off-On-Off-On-Off, seems silly, right ? So just turn up the allowable pressure setting. No don't, do this.

The way I see it, the first time the trip (or Cut-Out) pressure is reached, maybe 8 Oz. (13.8" WC) or less, the boiler gets shut off, then delay the restart with a timer maybe 5 to 10 minutes. So no more crazy pressure, no more short cycles. There are other Electrical / Electronic ways, like controlling the situation by limiting the fill time of the furthest radiator from the boiler then shut down the boiler and then delay the restart.

A timer is reasonably inexpensive and easy to install. Something like this is wired in series with the pressure switch circuit.

https://www.supplyhouse.com/ICM-Controls-ICM203FB-ICM203F-Delay-on-Break-Timer-6-Wire-Leads-03-10-Minute-Knob-Adjust-Delay

you tell us! If you don’t have any problems, then why is this thread here? 😂

As @ethicalpaul said, cycling on pressure won't make it take longer to heat the house — the radiation is doing all it can on the steam, which is still there, and that's what's heating the house. The extra fuel burned when the system should be cycled off so the system can catch up is just wasted.

Much the lesser evil is cycling. Cycling on proper pressure saves fuel and prolongs the life of all the elements in the system. What's not to like?

More energy is needed to make 5 PSI steam then 2 PSI steam. The oil burner must operate fonge to make 5 psi steam. if you stop the burner from operating when you have 2 PSI steam then you are not burning any oil. Now that you have 2 PSI in the steam boiler and the burner is off, you can let that steam pressure go to the radiators as long as the vents get the air out of the way. Of course that 2 PSI steam will find its way to some place to give off that heat and condense, resulting in a pressure drop that will bring the burner back on. but that burner off cycle is saving on fuel cost. If you left he burner on and raised the pressure to 5 PSI, that will not get the radiator to heat any faster and that higher pressure steam will not heat that room any faster. All that higher pressure steam did was use up more fuel… it did not heat the radiator any faster or heat the room any quicker. All that higher pressure did was to use more fuel with no actual benefit to comfort.

A number of possible reasons… first, not all systems operate well at a maximum pressure of 1.5 to 2 pounds. Vapour systems, for instance, get unhappy at anything over half a pound (so they use a similar but more sensitive device called a vapourstat). Many larger systems will have two or even sometimes three pressuretrols. One — likely a vapourstat again — for system cycle control. One, set higher, as a safety control. And some have a third, often manual reset, as a further safety control set significantly higher.

Then some steam systems are used with some types of air handlers or unit heaters which need higher pressure. Others (such as breweries) run higher pressures because the need higher temperatures.

And so on…

Or install a 0-3psi gauge and SEE what's going on.

" When do you vary from that? "

Hopefully never, at least with residential steam heat, you don't need the pressure, why pay for it. Get a functioning Gage or two on the system and see what the system is really doing.