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Help troubleshooting my boiler.


Tom Raymond
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I woke up to a cold house this morning, well half the house was cold anyway.

I have a gas boiler about 12 to 15 years old, I do not know what make and I'm not there now to check. It has 3 zones each with it's own Honeywell thermostat (old school mercury switch) and zone valve ( I know because I installed them). All 3 zones were calling for heat, all 3 valves were open, the burners were running with clean flames, the system temp and pressure were normal (60 psi, 160 F). One of the 3 zones reached the set temp and the boiler shut down while the other 2 zones were still 6 and 8 degrees colder than the set temps. The satisfied zone vale closed, but the other 2 remained open. I manually opened the satisfied zone valve, but the system didn't refire and the circulator pump did not restart. There were good temp differentials on the supply and return lines when the system shut down. The only unusual set up is the mixing valve for the hydronic tubing on one zone, the other zones are cast iron radiators running at full temp. I keep the house cool, the in floor zone is set at 62 F, the downstairs radiator zone at 64 F and the upstairs zone (this is the zone that is functioning) between 64 and 66 F. All of the zones slightly overlap as there are only open archways and a stairwell between zones, none can be closed of from the next, and the slight difference in temp settings keeps all the zones firing independantly (if they are all set the same the system tries to run on the in floor loop only and I have cold spots).

I think it highly unlikely that 2 zone valves failed simultaneously. I also think it unlikely that the controler is bad if one zone is still functioning. I only had about 15 minutes to mess with it this morning before I had to go to work. I have a very good plumber I call when I need help or can't fix it myself, but he has not returned my call yet today. Any ideas as to what is going on with this system?

Thanks,

Tom

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I take it the boiler is a hydronic system, not steam? 60 lbs at 160F is not normal. Most boilers have a 30# pop with a 12# city water makeup reducing valve. At best their running 26, or so, lbs at 200F. Have you changed out your safety valve for some reason? What is the boiler rated for pressure wise?

To the problem:

Can any of these zone valves call for heat through an auxiliary switch? The stat can open and close the valve but how is a call for heat initiated? Once a call for heat is initiated what is the controlling thermostat? Does the boiler have a operating thermostat and a hi limit safety?

Is the boiler on an indoor outdoor reset of some kind?

Obviously a VOM will find the open circuit which is what will be needed to troubleshoot.

I'm concerned about the 60# pressure though. Something doesn't seem right here. Only time I've seen boilers with that high of an operation pressure is in a multi-story office building.

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Hi Tom,

Could the unresponsive zones be air locked? I see those systems rarely here but on more than a few when they didn't respond in one area of a house I just opened the bleed valves, put a rag under the valves, and then waited for the air to stop hissing and the valve to pee a little bit before I closed the valve. After that, they worked fine.

I have no idea if I'd broken some kind of taboo, only that it seemed to fix the issue. I told the clients that if that situation repeated itself that they'd need to ensure that a boiler pro checked the system out and fixed it. I'd encouraged them to come back to the house in a day or two, fire up the system and wait an hour to ensure that it was heating evenly - if not, ensure that the system was checked and fixed prior to closing.

Since I've never heard from any of them, I've always assumed that bleeding the air out of the system did the trick.

ONE TEAM - ONE FIGHT!!!

Mike

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Terence, the boiler always runs between 55 and 60 psi at temperature, I think the hi limit is 180 F.

Chad, there is one transformer at the controler, the t-stats are wired to the zone valves, the zone valves all connected to the controler. If the transformer was bad, wouldn't all the valves be dead?

Mike, the iron radiators burp really loudly when the need to be bled, and the tubing had good temp differentials and an integral air scoop so I think they are ok.

Jim, the controler is mounted on the lower right corner of the boiler with the zone valves front and center about 18" higher than the top of the unit, the wiring from the controler to the valves is about 3' max. and appeared to be fine.

I will test the T-stat lines when I get home.

Thanks.

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Originally posted by Tom Raymond

Mike, the iron radiators burp really loudly when the need to be bled, and the tubing had good temp differentials and an integral air scoop so I think they are ok.

Than let me suggest one other possibility that I neglected to mention - they're just plain clogged up with rust like my arteries and aren't allowing any water through.

I remember reading an article a few years ago; can't remember where - possibly Old House Journal - where they talked about how old cast iron radiators are often so inefficient because they're so full of rust. I think the author said that the only way to really fix them is to remove them, take them to a place that will acid dip them to remove the rust and then will rebuild them by installing new segment compression donuts, new valves, and new seals where needed.

I guess that is frought with problems too, because the author said that the compression donuts were no longer being made and one supplier had bought up all remaining stocks in the country years ago and was slowly running out of stock.

So, maybe it needs a bioplasty or whatever it's called to clear the arteries.

ONE TEAM - ONE FIGHT!!!

Mike

P.S.

Jim's comment about it being more a brain thing than a body thing struck too close to home. Every day I see more and more that something, dunno what - too much coffee maybe - is killing off the old brain cells. Pretty soon they're going to be entertaining me with Fisher-Price toys - it's Benjamin Button without the younger body. [:-dopey][:-drool]

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I don't think it's a clog in the radiators. Thay are old, but not original to the house. I bought them from a salvage place, refurbed them and installed them about nine or ten years ago. I know there is sediment in the system though because I can see it in the pex tubing. I don't think the tubing is blocked because of the good temp differentials, but I could be getting some temp bleed from the mixing valve if they are.

I am hoping it is something simple like a loose wire, or such. Still have'nt heard from my plumber, so I will be playing with it when I get home around 4pm. I'll post what I find if I can figure it out, otherwise I'll be looking for someplace warm to sleep tonight. Anybody got a spare room?

Tom

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Don't mean to sound like chicken little Tom but I'd call the boiler manufacture, with the model number of the boiler, and ask them what size relief valve should be on this boiler. I've never seen a residential boiler with more than a 30lb relief valve. You shouldn't need more than 20lbs of pressure to have good flow through out the home (unless you're living in a 50,000 sq ft home).

If you installed the HW zone valves I'd look at the specs as well. Most motorized zone valve have a water inlet pressure operating range. They may not operate correctly with a 60lb inlet pressure.

Bell& Gossett boiler PDF (very basic).

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OK. Terence, your concern over the pressure has me second guessing my memory. The guage on the boiler is in psi and kpa. 60 kpa would be about 8 or 9 psi. I could have mixed these up in the several hours between looking at the boiler and posting here, it is very frustrating trouble shouting anything in my PJ's and worse when I am late for work. In any event the guage is well within the normal range it has been operating in for the last ten years. It has been serviced twice in that time frame by a professional. If the pressure was dangerous I would think he would have caught it.

Now, the lower pressure may change some of the thoughts on this thing.

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Is this the correct sequence for the system?

Thermostat calls for heat.

Zone valve opens.

Circulates water.

Water coming back to boiler becomes cool, burner fires to warm water.

Continues to circulate.

Thermostat satisfied, all shut down.

If by design you have two wires coming from each stat back to the controller, remove each stat one by one at controller and jump it out , to see if the burner will fire once the water needs to be heated. I don't think it's the boiler because it comes on for zone one, so I think it's what Jim Katen said, control wire or a bad controller. You may be able to switch the wires on the controller to work a zone that is not functioning now, this will allow you to have heat in the living area or bedroom tonight.

ps: Its my understanding from your post that one zone functions fine. Is this correct?

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Originally posted by Tom Raymond

OK. Terence, your concern over the pressure has me second guessing my memory. The guage on the boiler is in psi and kpa. 60 kpa would be about 8 or 9 psi. I could have mixed these up in the several hours between looking at the boiler and posting here, it is very frustrating trouble shouting anything in my PJ's and worse when I am late for work. In any event the guage is well within the normal range it has been operating in for the last ten years. It has been serviced twice in that time frame by a professional. If the pressure was dangerous I would think he would have caught it.

Now, the lower pressure may change some of the thoughts on this thing.

The boiler, sitting at room temperature, should read 12 lbs pressure. If the expansion tank has a sight glass it should be 1/2 full (or there about). As you heat the water the boiler pressure goes up (but should not reach 30 lbs) and the expansion tank level raises a bit .

I've been involved with quite a few boilers where the pressure relief valve has been change out due to the correct sized one always weeping. When a service tech does not know how to troubleshoot they install a higher pressure safety valve to solve the problem.

If you're down around 9 lbs at 160F you have the opposite problem :)

Chances are the city water makeup valve is not allowing water to enter the boiler. Manual shut offs closed, dirty screen in city water reducing valve, valve not adjusted correctly to name a few. This would manifest itself in the fin-tube or radiators at the furthest runs being cold. Might even be tripping a low water cutoff in the boiler which would be the answer to your problem.

With regards to some tech catching a problem I wouln't assume that. Let's just say some are better than others - as in all trades.

As to the original problem if the boiler is not firing and the controls are calling for heat your going to need your volt meter to find the open circuit.

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Well, I have a few things figured out, the first of which is that I shouldn't try to remember a boat load of numbers while I'm still in my PJ's and before my morning cuppa Joe.

The pressure at 160 F is 200 kpa, or about 28 psi, not the 60 psi I thought I remembered and not the 60 kpa I was guessing because I made Terry nervous, and he scared me into thinking the thing was a ticking bomb.

My plumber finally called me back about 45 minutes ago, and asked "you have honeywell valves right?" he remebers all kinds of stuff about systems he hasn't seen in years. He told me that they are prone to stick in systems that have either high sediment city water (that's me) or anti freeze, and that the motors cannot open the valves far enough to trip the end switch and call for the burners to light.

He was partly right. It is a problem with the motors. I removed one and the valve turned freely, but the motor couldn't trip the end switch even without the valve connected. What I have is 2 defective motors with stripped gears, that will only reach the end switch if I manually open the valves and the t-stats call for heat from there.

So the good news is I know what is wrong, tomorrow is supposed to be much warmer than today (-5 F this morning), and the system will limp along ok until I can get new valves and swap out the motors tomorrow. The bad news is that out of the 3 valves, 2 are about 10 years old (put in when I did the radiators) and 1 is about 4 years old (done when I put in the pex) and the failed valves are one old and one new. Hopefully the last old valve will continue to function for at least another 48 hours or so, so I won't be running this thing manually until I can get the new motors and install them.

Thanks for all the insight,

Tom

Terry, I'll try not to make you nervous any more. Or at least write down what I think I see next time.

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Glad to hear the results Tom. So often when discussing problems you never hear the outcome.

28 lbs @ 160F the pressure is still high. While you're replacing the defective valves it would be a good time to properly fill the boiler. There is a screen on the city water reducing valve that should be cleaned too Tom. It is accessed from the bottom of the valve. After a while they get clogged.

Honeywell hasn't changed the design of the zone valves much if any (at least up to 2000 when I got out of the trades). You should be able to keep the valve body in place and just replace the guts (as long as the valve body seat is not worn too badly). If I remember correctly there are 4 screws to remove to pop the top. That way you don't have to cut and sweat in a new one.

Good luck!

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