Any boiler techs here?

[yooper]

I have natural gas hot water heat, like most people up here in the North. It came with the house. The boiler is a Crown "Aruba XE".

We've been here four years. Two years ago the boiler started this rapid cycling thing. I don't think it was doing it before. What happens is that when the boiler first fires up everything seems to work fine, but after it heats up a bit it will shut itself down every 10 seconds and start back up. There's a loud click, the flame shuts down, then after a few seconds it re-lights itself, burns for about 5 seconds, then shuts down again. One complete cycle, shut down to shut down, is about 10 seconds.

In this town the plumbers do the service on boilers. Maybe this is common, I don't know. Anyway last year we called the plumbers that had originally installed it (their name and number is on the wall) and they spent about 10 service hours messing with it, coming back twice, finally replacing what I think is some kind of temperature sensor that's part of a safety shutdown circuit. It started rapid cycling again pretty much right away but I was tired of throwing money at the plumber so I gave up.

This fall I called a different plumbing company. I wasn't home when he came. He told Mrs. yooper that everything checked out and was working fine, and just charged us for an annual preventive maintenance call. I haven't bothered calling to bring him back.

So my question is, is my boiler supposed to cycle every 10 seconds? It would seem to me that this is very inefficient, since gas is wasted at every re-light. Also it's hard on all the various switches and valves and solenoids. Just doesn't seem right.

I would like to fix this myself but have no experience and don't quite know where to start. I am comfortable with basic electronic circuits and mechanical stuff and plumbing and gas and fire. I just don't know any details about how boilers are regulated. Any suggestions would be helpful. If anyone has a Crown Aruba XE service manual that I can borrow or copy that would be sweeet.

thanks!

 

[Capt. Jim]

Not many boilers down here in South Florida, Yoop, and I have no experience with them. But if I were you, I would look at your thermostat. That is what sends the signal to the system to trip on/off. Perhaps some of the HVAC guys can help.

 

[SteveO]

When you hear it re-light has the flame actually gone out or is the ignitor just trying to relight?

If the flame is actually going out I'd guess it's tripping on high-limit or else the aquastat is wired wrong with the high limit wiring going through the wrong contacts on the switch.

If the gas doesn't go out but it keeps trying to re-light I'd say clean off your flame rod. It senses the flame and if it's dirty then the ignition system may keep trying to relight every 11 seconds on some models of ignition modules.

If you can get more info I can help you through it. ...Steve

 

[SteveO]

Also, if you can, post a pic of the wiring to the temp switch. ....Steve

 

[yooper]

Thanks Capt. but there are 8 thermostats. It's a zoned system. And with this kind of system the thermostats that you're thinking about just open valves and do not control the boiler itself. The control of the boiler firing is automatic and based on the temperature of the water in the system - it's a very complex thermostat basically.

 

[yooper]

SteveO the flame goes out. I'll go take a pic now. I think there is actually a schematic...

 

[rusty_tlc]

Sounds like the hysteresis setting/circuit is messed up. Most thermostats have a range on each side of the set point before they cycle. (EX: set point is 175°F and the hysteresis is 15°F the thermostat will turn on at 160°F and off at 190°F.) Google your model of water heater and see if there is a manual on-line that helps.

 

[SteveO]

I just re-read your first post and you said that it just started doing it a couple years ago. I guess that rules out the mis-wiring of the switch.

My next theory is it could be a bed end switch in one of your valves. Does the cycling happen when a certain valve is open or for any of them?

 

[rusty_tlc]

When you hear it re-light has the flame actually gone out or is the ignitor just trying to relight?

If the flame is actually going out I'd guess it's tripping on high-limit or else the aquastat is wired wrong with the high limit wiring going through the wrong contacts on the switch.

If the gas doesn't go out but it keeps trying to re-light I'd say clean off your flame rod. It senses the flame and if it's dirty then the ignition system may keep trying to relight every 11 seconds on some models of ignition modules.

If you can get more info I can help you through it. ...Steve

I think we call the flame rod a thermocouple here in the US. For a standing pilot system it will not allow the gas solenoid to open if the pilot is out. For direct spark ignition systems my understanding is it shuts the gas solenoid off if the flame dosen't light.

 

[SteveO]

I think we call the flame rod a thermocouple here in the US. For a standing pilot system it will not allow the gas solenoid to open if the pilot is out. For direct spark ignition systems my understanding is it shuts the gas solenoid off if the flame dosen't light.

A standing pilot system will have a thermocouple that produces a small voltage to keep the pilot valve open but a direct spark ignition system doesn't usually use one. A flame rod will use a process called flame rectification to prove to the ignition module the presence of flame by passing a current from the rod, through the flame into the burner. Often the flame rod will get a carbon coating and need to be wiped with an emery cloth to help it conduct.

You are right though about the direct spark system. It will try to light the flame for 11-22 seconds and then lock out if the flame doesn't light. ....Steve

 

[yooper]

I just re-read your first post and you said that it just started doing it a couple years ago. I guess that rules out the mis-wiring of the switch.

My next theory is it could be a bed end switch in one of your valves. Does the cycling happen when a certain valve is open or for any of them?

I'm uploading photos now. As far as I can tell it's the same with all of them, but why would a zone valve switch affect the boiler control and make it rapid cycle?

I think they replaced the pilot module with its thermocouple last year. The first thing they did last year was replace the ignition module, but that didn't help...


Rusty, I was thinking the same thing about the hysteresis of the control - maybe I just need to adjust this, but looking at the circuit schematic hasn't been very helpful in this regard.

Still uploading photos...apparently I had over 100 in the camera that I haven't uploaded yet and it only works as a batch...will post ASAP.

 

[SteveO]

I'm uploading photos now. As far as I can tell it's the same with all of them, but why would a zone valve switch affect the boiler control and make it rapid cycle?
.

If you have 4 wires to each of your valves two of them are an "end switch". Tehy're use dto start the boiler and sometimes the pump once the valve is fully opened. On lots of systems the t-stat controls the valve and the valve controls the boiler. Not saying that's tru of yours though, almost every system is a little different and there are a ton of ways of wiring them. ....Steve

PS. I'm off to dodgeball but I'll check the thread later tonight when I get home. Hopefully you'll have it solved by then Good luck. ....Steve

 

[yooper]

Schematics were difficult to photograph - lots of pipes in the way, what's with that?

shematics and ignition module:

 

[yooper]

If you have 4 wires to each of your valves two of them are an "end switch". Tehy're use dto start the boiler and sometimes the pump once the valve is fully opened. On lots of systems the t-stat controls the valve and the valve controls the boiler. Not saying that's tru of yours though, almost every system is a little different and there are a ton of ways of wiring them. ....Steve

PS. I'm off to dodgeball but I'll check the thread later tonight when I get home. Hopefully you'll have it solved by then Good luck. ....Steve

Kinda complex system. 8 zones I think. 6 of them are on a zone priority control box, to give priority to the hot water maker. One zone is a "low temp" thing, with I think its own pump, that controls the floor heat in one bathroom. The Taco valves all have three wires each. The Low Temp box has four.

If any of the zones are causing it, I think I'd blame the Low Temp the most, but I've watched this thing over and over and it seems to exhibit the cycling behavior independent of which valves are open.

Here's a pic of the old replaced part from last year. Pretty sure it's the spark igniter and thermocouple:

 

[albee]

I had a bad connection to one zone. The hot water that was heated for that zone just went thru the primary loop and back into the boiler. Since the water was still hot the boiler short cycled untill it cooled enough to restart the boiler.

Call tech support at the place that makes the boilers. Mine broke a few weeks ago, and ended up just being and exaust fan. A plumber told me $800 in parts plus labor. No thanks I will just replace the $60 fan and see what happens. Everything is warm again in my radient heated house. Albee

 

[yooper]

Since the water was still hot the boiler short cycled untill it cooled enough to restart the boiler....

Trying to wrap my brain around that. I don't get it.



x100 on forgetting about the plumber though. I spent a LOT of money on the plumber and it was a total waste.

I found the manual online. This sequence of operation tells me that either it's the high limit circuit or the pressure switch circuit for the blower. I should be able to measure each one of those circuits during the suspect behavior and isolate the problem one. I think... the high limit makes more sense because it doesn't happen until the entire boiler has been on for a while, i.e. the first time it fires up it will burn for a good 10 minutes before it starts short cycling...

 

[yooper]

With the help of the manual I was able to find the hi limit control box and the pressure switch.

The pressure switch works fine, and when take it out of the circit and I short its connection with a jumper wire the boiler still short cycles.

Nothing (voltage, resistance, current) changes across the contacts of the high limit thingy, and I turned up the high limit by 5 degrees while it was short cycling, with no effect.

There are two sets of wires going to the "thermostat" connectors in the control box. One is coming from the priority zone control box, which is pretty new, newer than this short cycling problem (the plumber that installed the priority box is the one that spent three service calls on this problem last year - we had the hot water maker installed at that time). The other wire goes to the In Floor heat controller for the bathroom floor.
To get the system to turn on I opened three Taco valves manually. The In Floor unit did not come on and I still got short cycling. The cycle period was 8 seconds tonight...

 

[yooper]

Again, it doesn't start rapid cycling until it heats up a bunch. Tonight it took about 5 minutes before it started short cycling...

 

[yooper]

Time for bed. I think I'll "clean off my Flame Rod" first.

 

[TheJackRabbit]

Shoot, when I read title of this tread I thought Yooper was converting to the first steam powered Land Cruiser- you know, boiler in the back and low and high pressure reciproacting cylinders under the hood with a flywheel about five feet in diameter. I can just see him behind he wheel with the wife tossing logs into the firebox and complaining about her nails.