# Short Cycling Boiler?



## matt151617 (Jun 26, 2011)

Recently my 7 year old Weil McLain boiler has been short cycling; it turns on every few minutes, runs for a minute or 2, and shuts off. This has resulted in huge oil usage: 1/4 of a tank in 9 days. My house is 1 story 1500 sq ft, divided into 2 zones. It has been cold but I keep the main zone at 64 degrees for about 5 hours a day and the rest of the time at 60. The other zone stays at 61. 

The main zone thermostat has an energy usage tracker and shows the thermostat has been switched on an average of 8 1/2 hours a day. The boiler itself has the aquastat hi set at 185, lo at 110, and diff at 10. There is a DHW coil installed but it's no longer used (pass through only). The boiler was cleaned and serviced last month and tested at 85% efficiency. The house also had an energy audit and no major leakages were found. 

What is going on here? At this rate, I will use close to an entire tank in a month, about $650.


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## biggles (Jan 1, 2008)

185F setpoint those baseboard/rads should be cookin' is the body of the circulator pump supper hot sounds like the water isn't getting cycled and just sitting.


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## matt151617 (Jun 26, 2011)

All the radiator pipes, including the radiators themselves, are far too hot to even touch. Comparing the feel of the 120 degree hot water pipes, they're definitely much hotter. 

I can verify pipe temperature with an infared thermometer but judging by the occasional thump sounds of the pipes against the floors, they're definitely transferring heat.


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## biggles (Jan 1, 2008)

your boiler isn't maintaining the water during a no call for heat except for the domestic hotwater call for 110F..right.was that 185F always like that seems high for baseboard to make even 68F stat settings


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## Missouri Bound (Apr 9, 2011)

Measure the temp of the supply and return pipes...and all of the registers. Did this start happening? Sounds like the circulator isn't doing it's job and the hot water just isn't moving enough. Any closed zone valves?


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## matt151617 (Jun 26, 2011)

What's a better HI temp setting? I read a few blogs that said 200, that the really hot water transfers heat into the room better, but I thought that was too high.

The boiler is maintaining the heat... by watching it, it looks like it lets the temp drop about 10 degrees below the HI setting before turning back on for a minute or so to reheat the water. I'm wondering if this is where the waste is coming from, since it has to kick on fairly often.


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## AandPDan (Mar 27, 2011)

180 is a fine temperature for baseboard heat.

When did you "pass through" the dhw coil? 

Is your boiler staying hot all the time? If you aren't using it for water it should have been converted to cold start. It does not need to maintain a specific temperature.


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## matt151617 (Jun 26, 2011)

In July I "bypassed" the DHW coil; I plumbed an electric hot water heater after the coil. So the water enters through the coil, exits, goes to the electric hot water heater, exits that, then goes to the house.

During the summer I just shut off the boil. With the LO set to 110 (that's the lowest I could get it), it doesn't kick on much. I contacted Honeywell (aquastat manufacturer) about how to totally disable the LO and DIFF, but they'll only provide information to contractors.


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## beenthere (Oct 11, 2008)

You should have bypassed the coil all together. Every time you use hot water, your cooling your boiler down, so it still uses oil everytime you use hot water in the winter.

8.5 hours a day? For one zone?


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## AandPDan (Mar 27, 2011)

biggles said:


> 185F setpoint those baseboard/rads should be cookin' is the body of the circulator pump supper hot sounds like the water isn't getting cycled and just sitting.


Check this.

Your house should be roasting with 180 degree water and it cycling every two minutes.


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## matt151617 (Jun 26, 2011)

Sorry, wrong terminology... by cycling, I meant the boiler itself is firing up, then shutting off.

I checked the boiler temps the other day but it isn't accurate, it was warmer and the boiler had cooled off a lot. 

The last few days have been average temperature. The thermostat shows about 3 hours a day of run time. The 8 hour day was extremely cold outside and I had it turned up to 66 degrees the whole day since I was home.

Still, 1/4 of a tank of fuel usage in 9 days seems extremely high...


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## AandPDan (Mar 27, 2011)

matt151617 said:


> Sorry, wrong terminology... by cycling, I meant the boiler itself is firing up, then shutting off.


That's a cycle, start - stop.

3 hours a day, what's your nozzle size? You're only talking maybe 3 gallons with a 1 gph nozzle. That's 27 gallons, make it 32 with one 8 hour day. 

No where near 1/4 of a typical tank.

How long does it run, then how long is it off for? Do you have to reset anything when this happens or does it just continue on its own. If you turn the 'stats off, will it still cycle?


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## matt151617 (Jun 26, 2011)

Here's what I found. The pipes going to the radiators were testing at 134 degrees, but I think that's wrong. The radiators themselves were testing 155-165. The main connection on the pipe leaving the boiler was 185, temp gauge on the boiler showed 190.

I think I discovered the problem. The thermostat switches on, and stays on till the temperature matches the set-point. However, the boiler doesn't do this... it turns on, runs until the temp hits 190, then shuts off and circulates for awhile. So when I look at the run time on the thermostat, it's not really representative of the true run time of the boiler. Especially since it takes awhile for the rooms to heat up.

I think the nozzle size is .8 gph. All I can gather is sub-zero temperatures in combination with me being home all day really put a strain on the oil in the tank. Also even though the tank read full on the gauge, maybe it wasn't 100%, and that first 1/4 dropped a little faster.

It seems to run for about 2 minutes, then shut off for about 4-5 minutes (while the thermostat is calling for heat). It runs on its own and I've never reset anything. When the thermostat is off it doesn't do anything.


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## Missouri Bound (Apr 9, 2011)

The pipes going to the radiators should be closer to the boiler temperature. I'm still thinking you have a circulator problem. What's the boiler pressure?


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## matt151617 (Jun 26, 2011)

Missouri Bound said:


> The pipes going to the radiators should be closer to the boiler temperature. I'm still thinking you have a circulator problem. What's the boiler pressure?


Understood, I think it's just a crappy infrared thermometer not reading the pipes correctly. I don't think it's possible for the pipes going to the radiators to be colder than the radiators themselves.

No clue on the boiler pressure, the gauge is apparently broken. It's reading 42 psi, which is obviously not right. The PRV is set for 30 psi. Pressure gauge reads 42-40 psi even when the boiler cools off. I will change it out in the summer when it's shut off.


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## AandPDan (Mar 27, 2011)

Your boiler is hitting the high limit, 190, and shutting down. The circulators are still running because the thermostat is calling for heat.

You need to fix that pressure gauge. 42 is dangerously high. I know, the PRV is set for 30 but how do you know it works? Too little pressure isn't good either.

The pressure can be part of the problem.


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## Missouri Bound (Apr 9, 2011)

AandPDan said:


> Your boiler is hitting the high limit, 190, and shutting down. The circulators are still running because the thermostat is calling for heat.
> 
> You need to fix that pressure gauge. 42 is dangerously high. I know, the PRV is set for 30 but how do you know it works? Too little pressure isn't good either.
> 
> The pressure can be part of the problem.


 
yeah....you have got to get everything in working order before you can diagnose this problem. How long has that gauge been bad? You are asking for a serious problem if you ignore the basic safety issues.


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## matt151617 (Jun 26, 2011)

It broke probably in the last couple weeks. I'm not really sure what's involved in replacing it, but I'm assuming I have to partially drain and refill the boiler... not sure how to do that.


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## Missouri Bound (Apr 9, 2011)

matt151617 said:


> It broke probably in the last couple weeks. I'm not really sure what's involved in replacing it, but I'm assuming I have to partially drain and refill the boiler... not sure how to do that.


 
I hate to tell you this but I'm thinking you are in over your head. Time to get a professional to check out your system. If you attempt to work on it yourself you just may get yourself hurt.


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## AandPDan (Mar 27, 2011)

Matt,

I agree with Missouri, call someone in.

The high limit is a safety device and you're up against it. That shouldn't happen in a properly functioning system. You don't know what the boiler pressure is as the gauge is reading dangerously high. The PRV may not be working either. Is it the gauge/PRV or both?

Replace the aquastat with the correct, cold-start, unit and get rid of the "bypass" on the DHW coil. You're using a lot oil to keep the boiler warm just to preheat the water for the electric water heater. 

Tankless coils waste energy. A better option would be an indirect off your boiler. It can make a lot of hot water, very fast. Run it as a zone on your system. The boiler would still be a cold-start, just firing when called. Indirects tend to last a very long time and are very well insulated.


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## matt151617 (Jun 26, 2011)

The gauge is separate, and the PRV is marked 30 psi. I could test the PRV and see if the pressure drops but I won't touch anything; I'll call the oil company tomorrow and have them come take a look. It happened right around when they did an annual tune up so maybe they'll fix it for me. They may also know how to make the aquastat into a cold start, if that's possible.

Maybe I'll re-plumb and bypass the coil for now. The hot water heater is brand new and I'd hate to just waste it.


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## AandPDan (Mar 27, 2011)

Don't test the PRV. For one thing, you have no good way to test it, short of it opening. Your pressure gauge reading may/may not drop. If it is sticking, and you open it, you'll have a mess to clean up.

Leave well enough alone.

It's funny this happened when you had the boiler serviced. They should have checked out the operation of the entire system.


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## matt151617 (Jun 26, 2011)

I called the fuel company and they recommended letting the boiler cool off, then open the PRV just for a second. They also said they would come over and do it for me if I wasn't comfortable trying that. 

So if the PRV functions properly it's probably the gauge. 

As far as I remember the pressure gauge was functioning fine at the time of the maintenance.


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## AandPDan (Mar 27, 2011)

Lets just hope it is the gauge.

Let us know how it goes. Good luck.


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## bubbler (Oct 18, 2010)

matt151617 said:


> It happened right around when they did an annual tune up so maybe they'll fix it for me. They may also know how to make the aquastat into a cold start, if that's possible.
> 
> Maybe I'll re-plumb and bypass the coil for now. The hot water heater is brand new and I'd hate to just waste it.


If you have a full service oil company with a service contract those types of repairs (gauge) are often covered. I know for mine I pay them a couple hundred per year and they'll fix anything to do the with the system short of replacing the boiler block or DHW coil.

For the new tank water heater, it won't be wasted... you'll just feed it directly from a cold supply instead of from the output of your DHW coil in the boiler.

You should have the oil comapny replace your aquastat for that btw, they will put in a cold start one... the one you have now can't be set for cold start.

BTW slightly off topic on the pet peeve of people who call it a "hot water heater", I think this is one instance where calling it a "hot water heater" is actually correct! You are literally plumbing the hot water from your DHW coil into the tank water heater :laughing:


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## matt151617 (Jun 26, 2011)

Hit the PRV and it started blowing a bunch of oil tainted water out. Quite a lot came out, and stopped once the gauge hit 30 psi. Scary, this thing really was ready to blow. Glad no one got hurt. 

What do I do now? Can I turn it back on?


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## AandPDan (Mar 27, 2011)

30 is still to high, it should be about 12-16.

What's the pressure now?

Get someone in to service the system. The PRV should have never have let the pressure get that high, it was sticking. It needs to be replaced ASAP - it is a safety item.


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## matt151617 (Jun 26, 2011)

It's at 30 psi, temp is at 120. I suppose I could get the pressure down more by holding the PRV open, but won't the system be full of air then? I will have someone come out tomorrow, but what should I do for tonight? It's supposed to be single digits, and I can't leave the boiler off all night.


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## TarheelTerp (Jan 6, 2009)

matt151617 said:


> It's at 30 psi, temp is at 120. I suppose I could get the pressure down more by holding the PRV open...


the ISSUE is that it shouldn't be running up to that pressure



> ...but won't the system be full of air then?


No specific advice now...
but weren't your control issues all hashed out in another thread recently?


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## AandPDan (Mar 27, 2011)

You can drain off more water, just watch the pressure. 12-16 is what you should have.

The house shouldn't go below freezing in 12 hours. I know it won't be comfortable.

My take, the pressure was high, you have a sticky PRV, and you're bouncing of the high limit. I wouldn't feel comfortable leaving it on while I slept.

Good luck tomorrow.


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## bubbler (Oct 18, 2010)

matt151617 said:


> It's at 30 psi, temp is at 120. I suppose I could get the pressure down more by holding the PRV open, but won't the system be full of air then? I will have someone come out tomorrow, but what should I do for tonight? It's supposed to be single digits, and I can't leave the boiler off all night.


Have you called the oil company? They may have 24 hour emergency service...


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## matt151617 (Jun 26, 2011)

I got the pressure down to 10 psi and it seems to be holding there even while firing. I will monitor it closely and shut it off before going to bed, and get up in the middle of the night to turn it back on enough to heat the house again while watching it.

Thanks to all who helped and saved me from a potentially disastrous situation. Any idea how something like this could have happened? I understand the PRV is sticky but how did it end up getting so pressurized? The water coming out was pretty black so I'm wondering if that had something to do with it.


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## beenthere (Oct 11, 2008)

What caused the water pressure to get so high is the concern. good chance the auto feed is bleeding through.


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## matt151617 (Jun 26, 2011)

The boiler guy actually mentioned that. Well, lets hope it's not too expensive.


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## bubbler (Oct 18, 2010)

http://www.youtube.com/watch?v=rGWmONHipVo

Wonder what a boiler would look like :whistling2:


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## matt151617 (Jun 26, 2011)

Everything is good to go, they replaced the PRV and auto feed and everything is good, $98 total. Hopefully someone else can learn from this thread. 

Also, the oil is still close to 3/4 of a tank so the gauge must have a quick first 1/4. 

Many thanks to everyone who helped and urged me to get it checked out. I planned on leaving it till the spring and replacing the gauge.


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## Missouri Bound (Apr 9, 2011)

Cheap fix for a lot of worry. Glad it's taken care of....stay safe!


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## beenthere (Oct 11, 2008)

Your oil tank is not the same width at the top, as it is from the 3/4 down to 1/4 height. So the first 1/4 tank the gauge shows used, is very little oil compared to the next 1/4.

By gauge. 3/4 full tank is 223 gallons left, 1/2 full is 144, 1/4 full tank is 63, and 1/8 full tank is 23 gallons. this is for a 27 wide X 44 high tank.


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## matt151617 (Jun 26, 2011)

One more thing. Noticed now that I have no heat in one zone. Pipes and radiators in that zone are cold. Wires for that circulator all appear to be intact. What could have happened and is this anything I can take care of now before calling them back over in the morning?


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## beenthere (Oct 11, 2008)

Might have air in that zone. needs purged/bled out.


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## AandPDan (Mar 27, 2011)

Glad you got the other problems fixed.

Yup, it's probably air in the system.


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