Broken Pressuretrol - Next Steps?

merikus

I have a one pipe steam system that runs pretty good overall. Lately, I've noticed that during extended burns, all radiators will get hot fully across but the oil burner will still be going with no change in sound. This made me suspect a broken pressuretrol or clogged pigtail.

To attempt to diagnose this problem, while the boiler was running I used an instrument to lift up on the pressure plate switch until it clicked. I held it for about 10 seconds, and there was no change to the boiler. I considered trying to get it off to check the pigtail, but it seemed difficult and unnecessary given the switch experiment.

This leads me to think that I need a new pressuretrol--although I wonder if there could be a wiring issue with the current pressuretrol and have no clear way to diagnose that. After reading Dan Holohan's books, I think I may be better served by a vaporstat since I have to replace the thing anyway. This leads me to a few questions:

1. How dangerous is this problem? I think it's been running this way for awhile, but is this an immediate fix or something I can fix on the off season?
2. Are there any additional experiments I should perform to confirm my diagnosis?
3. Would I be better served by a vaporstat over a pressuretrol? Is there any additional information I could provide to help answering this question?
4. Can a vaporstat be installed at the end of a pigtail like a pressuretrol, or do I need to get more technical than that? Due to lack of local availability of contractors, this will be a DYI project.
5. How hard is it to install a vaporstat? I am a competent homeowner (e.g., installed my own smart thermostat) but get uncomfortable when I need to start doing things that are irreversible.
6. Is there a particular brand of vaporstat I should purchase? Is there any additional information I could provide to help answering this question?

Thank you all for your help and insights!

Jamie Hall

The problem is dangerous -- that pressuretrol is both a control and a safety device, and if it isn't working properly the boiler can reach much too high a pressure. So...

There is a simple check (but be careful -- you don't want to light yourself up). Lift one of the wires in the pressuretrol from its contact, and leave it free -- not touching anything. Now try to start the boiler. If it starts, you have a real problem with the wiring somewhere. If not, either the pressuretrol has a problem -- or the pigtail. So if that check passes, the next thing to do is to check the pigtail for being clogged. It's a common problem. Take the pressuretrol off the pigtail and see if you can pour water through it in a continuous stream. If you can, it's not clogged. If you can't -- it backs up and slops -- the pigtail is clogged and the pressuretrol can't see what's happening in the boiler. Take the pigtail off and blow it clear or run something -- a long zip tie works great -- and try to clear it. Also check where it connects to the boiler -- that sometimes clogs too. Worst comes to worst, you should be able to buy a new pigtail (I prefer brass). Put everything back together and see how it works.

If it still won't shut off on pressure from the boiler, then you do need to replace the unit. Since you've already had it off to check the pigtail, you have a pretty good idea as to how to proceed -- but be sure to mark, clearly, which contact screws in the old pressuretrol go to which wires. Step by step photos are cheap and help a lot!

Would you be better with a vapourstat? Maybe. Most one pipe steam systems don't need the extra precision and cost, however, so I wouldn't bother.

merikus

Thank you for your wonderful insights, @Jamie Hall. I opened up the pressuretrol and noticed there was a wire nut with two wires in it, completing the pressuretrol circuit. I opened that up, isolated the wires, and repowered the boiler. It went through its full ignition sequence so I guess that means I have a wiring problem. 

Upshot is that this means I’ve had a wiring problem for long before I owned this house, so I’m not in danger of blowing up. I’ll need to find an electrician as this is a bridge too far for me. But at least I know what the problem is so I can give pretty specific instructions to someone. 

Thanks again!

merikus

Well, @Jamie Hall, I lied--the electrical work wasn't a bridge too far for me.

Your wiring test inspired me to better understand how the boiler system is working. I read up on the wiring diagram for the PA404A (https://temperaturecontrolsystems.com/PDF/60-2341.pdf) and realized that my controller is the Carlin ProX 70200.

I read the manual (https://carlincombustion.com/wp-content/uploads/MN70200B-062819-Instructions-web.pdf) and learned in this video (https://www.youtube.com/watch?v=DMYBZUVuaWc) that the Limit In terminal only engages the system if there is power to it. This got me to think that there was some mis-wiring that was causing power to get to that terminal when the circuit was open.

So I opened up the junction box under the Carlin ProX, and what do I find? The Limit In terminal directly wired to the hot lead for the entire system! The pressuretrol circuit is powering an entirely separate circuit of my automatic water feeder--and was not connected to Limit In in any way. In other words, the critical Limit In terminal that switches off the boiler when power is disrupted to it--was wired directly into the hot lead, which will never lose power unless we have a power outage.

I moved the wire to the Limit In terminal to the neutral end of the pressuretrol circuit. Things are currently working, so I know at the very least that the pressuretrol circuit is remaining closed. I still need to do the other things we discussed (checking the pigtail and cleaning it out) but, for now, I have heat and a pressuretrol that is at least properly wired to the boiler limiter, so that's a step in the right direction at least.

Thanks again @Jamie Hall, you're a lifesaver to those of us who have to DYI our entire steam system out of necessity!

Jamie Hall

Bravo! And may I say I admire your initiative and work. Keep it up!

merikus

Continuing this tread in case anyone in the future is ever reading this trying to diagnose a similar situation.

One of the nice things I've learned about the Carlin ProX is that its screen shows LIMIT when the Limit In terminal is powered (thus permitting operation). This helped me diagnose that the wiring inside my junction box made no sense. The neutral of the pressuretrol was wired to a hot coming off of my low water cutoff. At first when I re-wired things I kept that connection between the pressuretrol neutral and the low water cutoff hot in a wire nut with a wire to the Limit In terminal, but this was causing the Limit In to never power off. So I wired that hot to all the other hot wires I had in a wire nut, figureing it had just been connected to all those wires by virtue of the pressuretrol neutral it was connected to 99% of the time when the pressuretrol circuit was closed.

Using the initial test that Jamie suggested of disconnecting the wires, I was able to verify that the circuit was isolated by observing the LIMIT display indicator. I also was able to verify that the pressuretrol switch does physically work by engaging and disengaging it physically with a tool.

My next fire will be the first time in a few decades that my system has had a properly wired pressuretrol circuit. Should be interesting. I still need to verify that the pigtail is clean and the pressuretrol actually works, but it's nice to know things are wired correctly (even if I am still a little trepidatious about whatever was going on with that random hot).

EBEBRATT-Ed

I would download the wiring instructions for the Carlin control.

It is imperative that the pressure control and any other limit controls like the low water cutoff be wired and working to be able to shut the boiler down.

This is a safety issue.

If the wiring is wrong it was probably done by whomever installed the Carlin control which is the brain of the oil burner.

When you get the carlin instructions make sure it is wired electrically to do what it is supposed to do. Then start the boiler and check that the pressure control low water cutoff service switch emergency switch (if you have one) shuts the boiler down

merikus

Thanks for this insight, @EBEBRATT-Ed. This actually helps me understand something that was going on with the wiring—but I’m not sure how to fix it. 

Since it was installed (20+ years ago?) the wiring went:

Main Power to Limit In (thus defeating the entire limiting system, since Limit In keeps a call for heat going unless there is no power to it). 

Main power to pressuretrol to a pink wire that goes in the direction of the low water switch. Two other wires come out of that same conduit going towards the low water cutoff—a pink wire connected to main power (in a wire nut with the Limit In jumper) and a white wire connected to neutral. 

My first step at re-wiring was simply to move the Limit In wire from the main power wire nut to the pressuretrol/pink-wire-to-low-cutoff wire nut. This did not work in controlling the limiter when I broke the pressuretrol circuit, indicating that the pink-wire-to-low-cutoff was powered. Since by virtue of it being connected to the non-functional pressuretrol circuit for 20+ years it was directly connected to main power, I put it in the main power wire nut. Your comment now makes me realize that the low water cutoff has no way of limiting the boiler. 

If I’m understanding this correctly, the low water cutoff circuit needs to be wired in series with the pressuretrol circuit, so if either lose power, it cuts power to Limit In, thus shutting off the boiler. At present, the low water cutoff remains defeated since I’ve wired both sides of the circuit to itself. 

Where I’m at a loss is how to do this. As I said, two pinks coming out of the low water cutoff conduit and one white. Both pinks currently wired to main power, white wired to neutral. There are two devices on the other side of the conduit in question: the LWCU and the automatic water feeder. I’m not sure which pink wire goes to which, or how to wire this in series so if one of the two safeties switches turns off, it will turn off all power to Limit In, thus turning off the boiler. 

What I need is Power-Pressuretrol-LWCO-Limit In. Problem is that I’m not seeing how to make sure if either pressuretrol or LWCO turns off, power to Limit In goes off, because it’s clear that power is coming through the LWCO. 

Maybe I should wire it Hot LWCO Pink Wire that I know is powered out of that conduit-Pressuretrol hot side-pressuretrol-pressuretrol neutral side-Limit In? But how do I test if my LWCO is functioning so I can make sure that breaks the circuit?

Any suggestions of next steps?

mattmia2

What model lwco is it? Get the instructions for that. The pressuretrol is just a switch, it can be in series with the power from the lwco to the limit so if the lwco cuts power OR if the pressuretrol opens, power to the limit is cut.

EBEBRATT-Ed

Get the Carlin instructions & the LWCO instructions. Make a drawing on paper the way it is supposed to be and post it here so we can see it then you will have something to follow.

Or call a heating tech or an electrician if you can't find someone else to fix it. It's a safety issue. Doesn't matter how long it's been that way

merikus

Thanks for the encouragement, all. The wiring issue has been dealt with. I’m having a hell of a time getting the pigtail off, though. It feels stuck on there. I’m thinking of having my local plumbing company open it up and install a low pressure gauge (0-3 psi) on the pigtail, so I can make sure it gets cleaned out and so I can monitor the pressure better than that 30 psi gauge.