Troubleshooting Buderus GC-124 Boiler

[75gmck25]

I have a five year old Buderus GC-124 gas boiler for my radiator hydronic heating, and it has an intermittent problem with starting up and running. It failed to heat up properly once last year, and happened again this morning.

This morning I found the pump running, but pumping water at about 100 degrees instead of the normal 135-140 degrees, since there was no flame. I turned the off the power at the local shutoff switch, turned it on again, and the boiler started up normally. However, the flame went out about 30 minutes later, before house temp got up to normal. I cycled power twice again before the flame started, and its running now, but I'm not sure it will keep running.

The boiler is pilot-less ignition, so I know there is a startup sequence and sensors that work when getting the flame going, and I believe there is also a sensor to ensure the electric flue damper is open (it was open, and I can watch the actuator move as the system starts up).

Anyone have any idea of what typically gets "tired" or dirty on this system and causes the burner to shut down? I originally thought it was failing to start, but now that I know it shuts down while running, there may be a problem with a sensor that operates when its already running. I can try disassembling the burner and cleaning everything, but that's a lot of time spent just for a shot in the dark.

I have a maintenance contract with a local company, and they will be here this afternoon. However, the guy they sent out the last time did not have experience with this specific brand/model, so the troubleshooting was very limited once it started up normally.

Thanks,

Bruce

 

[yeldogt]

That's a conventional atmospheric boiler -- I have used other Buderus CI boilers .. but not the 124. FYI -- the 124 is technically not a low temp boiler like all the other Buderus CI boilers .. so it needs slightly higher return temps. It's designed to replace conventional USA boilers running radiators and fin tube .. will do panels as well.

My Buderus boilers use Honeywell gas valves and limit switches -- it's all common stuff that any technician should be able to understand. When the Tstat calls for heat the flue damper opens -- when the damper reaches the end point it completes the signal path to the limit switch. The limit switch triggers by way of a relay -- to tell the gas valve to begin. The gas valve starts the ignition cycle.

Each thing is independent -- you need to see that the limit switch is staying "on" when the flame goes out. It may be faulty -- some limit switches have a connection for the damper ....others are wired in.

If the limit switch is on -- then it's the gas valve circuit. Ignition module or the actual gas valve -- or one of the safety's.

How are you controlling it -- simple thermostat? My memory is can't use Logmatic. The limit switch has an output for the pump -- all mine have Logmaticts that control the pumps,

Since it's not designed for low return water temp -- it may be condensing .... how do the burners look? They are SS .. and junk around? What's your return temp? how do you control the output temp (limit control?)

The limit controls go after a while as do the dampers -- I have never had to replace a valve or module ... but I'm sure they go as well. my oldest its getting to be about 25

 

[Jackfre]

When you say, "radiator" I am assuming conventional old CI radiator or hot water baseboard. Correct? If so, your return water temp isn't an issue, more than likely as they are higher temp emitters. Your sparker/flame rod assembly may be dirty. When electronic ignition came in and eliminated the pilot light they needed a way to signal that there actually is flame and that the gas valve is not spraying raw gas into the boiler. That standing pilot operation was replaced with the flame rod. Once the call is made thru the limits as YD describes, the control is looking to see if it is getting a microamp signal. The flame is actually the conductor. If over time the flame rod gets dirty the dirt acts as an insulator and you flame current signal becomes weaker and weaker. In that boiler (I had a 144 in my old home) that can also be affected by a down draft, where the pilot assembly is getting a reverse flow of colder air. Clean the pilot assembly. If that works I would get a new pilot assembly and at least have it on hand for the next go around.

 

[yeldogt]

Jackfre -- interesting to know.

I mentioned the return temp since it was discussed with me when I looked at the GC-124 a few years ago -- if the output temp is 135 the return may be too low for that boiler and he could have some soot or something.

I was going to install one until I was told it can't work with the Logmatic -- Conventional CI boilers are IMO the best for old houses (rebuilt or not) with radiators. I have two G224's running with almost no maintenance for 20+ years. The older one just needed a new indirect

 

[75gmck25]

My boiler has only a standard Honeywell setback thermostat, not the logmatic controller. I have cast iron, 1940 vintage radiators, all in one zone and with one Grundfos pump. Its a relatively simple system.

The repair guy went through the checks, and although it still works fine most of the time, he said it appears to be a problem with the Honeywell aquastat. The thermostat calls for heat and it turns on the pump and starts up the burner. However, sometimes the aquastat decides the water is now hot enough (it is set to 140), it cycles off the burner, and then the aquastat never turns the burner back on when it reaches the low set point (which appears to be about 120). Once it shuts off the burner it may just keep pumping water, which gets cooler and cooler because the burner does not cycle back on.

The aquastat is a Honeywell L7148F 1075, and I told him to just give me a price to replace it. However, Honeywell discontinued that unit and there is no direct cross-reference to a replacement. The best I could find with an online search was a refurbished unit. I'm not sure what the repair guy will come up with when he gets back to the shop and can look it up in his references.

Thanks,

Bruce

 

[yeldogt]

I would call Buderus ... they still sell the boiler -- what do they supply with the new ones?

.. otherwise do a search at the second hand suppliers

I'm sure someone fixes them .. also ...ebay is your friend.

 

[bobbyjean]

Raise low limit setpoint some.... See if it works... Looks like it is close to an oil type triple aqua stat ....Honeywell makes a universal replacement... They have a cross reference page.... Worth a look

 

[75gmck25]

The boiler has been working fine all day, but it always makes me uncomfortable when I'm not sure its really fixed.

I'm going to make some calls tomorrow to Buderus and to the local shops that install Buderus. They should have an idea of what part replaced the aquastat in my boiler.

I also found a supplier in NY (FW Webb) that seems to have a good stock of parts for Buderus and I'm going to call them to check on the cross-reference for a replacement. I'll be in upstate NY at the end of this week and would be able to stop by one of their locations.

Thanks,

Bruce

 

[75gmck25]

I confirmed with several supply houses that the Honeywell Aquastat is no longer availabe, and there is no direct cross-reference replacement. If I want to keep this model, the only option is a guy in Florida who tests and refurbished them for $180 +shipping. The catch is that I have to pull mine out and FEDEX it back and forth, so its at least 2-3 days with no heat.

My local contractor gave me this $945 option:
"Replace oem Honeywell aquastat that is no longer manufactured with new IQ hydronic control. The heart of IQ Control System is the Intelligent Hydronic Control.The control replaces the traditional separate ignition control, primary boiler aquastat, as well as the fan and circulator relays. The control stores two boiler supply temperaturesetpoints in its memory; one setpoint is for the High Limit Setting and thesecond is for the Operating Setpoint."

It looks like this IQ Control System is used on Burhham boilers, and maybe on other brands. I plan to call the contractor and ask if they have ever done this replacement, since it looks like it might require some skill to integrate it with the rest of my boiler controls.

I'm tending to feel that it may be better in the long term to move to the newer controller, since refurbishing the old one still leaves me with a part that is unreplaceable in the future.

Bruce

 

[bobbyjean]

HydroStat 3200 Universal Temperature Limit-see this on amazon...should work...check it out

 

[ToecuttersZ1R]

The HydroStat looks like it should work, supplyhouse.com is cheaper then Amazon.

https://www.supplyhouse.com/Hydrolevel-48-3200-Model-3200-Fuel-Smart-Hydrostat-Temperature-Limit-LWCO-Boiler-Reset-Control-for-Gas-Boilers

 

[yeldogt]

That's odd .. why would they use an odd controller? They only thing I can see is the front cover is not very deep ..maybe the typical Honeywell aqua will not fit -- they are deep.

 

[Jackfre]

Yeltdog, you are correct in the low return temp protection and with a 140* aquastat, there should be low return temp protection. If it was a fin tube baseboard system running at 180* it would not be necessary as your return temps would easily be over 140*.