Help with boiler not starting when cold

[pawel]

Not garage related but I need help please. We bought an old house in the spring and I have to fix the boiler. It will not fire all the time when it is cold. If I cycle the power on/off it will fire. At that point I can turn the thermostat down and up, it will fire every time. If it sits for an hour or more, it will not fire on the first try and I have to cycle the power again.

The draft inducer motor runs and the vent connected to the vacuum switch is clean. Both transformers are showing the correct voltage. I cleaned the flame sensor even though it did not look dirty. I pulled one of the electrical connectors of the vacuum switch and it fired right up as soon as I connected it again. I noticed when it won’t start, is that the draft inducer motor will keep running but it will not attempt to fire again.

Dunkirk model# GWB8-105IE
Series XEB-5

This is my first experience with a hydronic heating system. Any ideas what to check next?

 

[acmikee]

my guess would be that the ignition control is locking out and when you cycle the power it resets. so you either have a bad flame sensor or ignition control. I would by the whole control as it comes with a flame sensor and replace the sensor first than the module.

 

[pawel]

my guess would be that the ignition control is locking out and when you cycle the power it resets. so you either have a bad flame sensor or ignition control. I would by the whole control as it comes with a flame sensor and replace the sensor first than the module.

Thanks for the help.

I ordered the flame sensor this morning and supposedly it will be delivered tomorrow, so I'll give it a try tomorrow night.

When I looked at the ignition control it didn't say the flame sensor came with, otherwise I would have got it.

Any idea if I can use a different ignition module that restarts sooner than 5 min?

 

[Milton Shaw]

Check your vacuum lines and switches. May have one going bad, they are a common failure on 95% furnaces so I would suspect it on a boiler.

 

[naturalgas]

As stated above sounds like you need a new ignition module. You can use a Honeywell universal for intermittent pilot. Usually 3 try's then lock out. One thing to do is pull the hose of the vacuum switch and make sure the port at boiler end is clear.run a thin wire through it or tiny drill bit to make sure no crud is affecting it.


Sent from my iPad using Tapatalk

 

[Never Too Old To Learn]

Try cleaning the connections on the vacuum switch,make sure the vac. hose is not cracked,pressure switch will not work.Do not start replacing parts till you determine problem.A diagnosis of electrical,gas pressure and vacuum test at the vacuum switch is in order.The above suggestion concerning the vac. port is very good,also make sure port is not damaged on the boiler.

 

[75gmck25]

I had a problem like this once with my boiler last year, and the HVAC guy who came out showed me the diagram inside the boiler cover that explained the sequence of how it powers up and how it goes through the system checks.

In my case it appeared that damper on the vent was binding a little, and there was a safety interlock that prevented the ignition if the damper had not popped fully open. We could never reproduce the problem when the tech was here, so he just cleaned all the mechanisms.

I wanted him to clean up the burner also, but he was so unfamiliar with my boiler (a Buderus) that I was afraid to let him start taking it apart.

Bruce

 

[pawel]

Checking the vacuum port on the inducer motor was the first thing I tried. Port was not plugged and hose is in good condition and on tight.

Gas pressure is good cause my furnace runs great. How do I vacuum test the vaccum switch? I do have Mityvac pump kit, would that work?

 

[yeldogt]

What type of infighter ?

 

[bobbyjean]

wow-looks like alot hanging on the aquastat-fun to work on..... power down...
check everything for loose wires..if diagram is available ...post it here....if you already purchased the new ignition module you can try it...my two cents is the pressure switch...is the basement damp? if the problem happens each day...you can jump that switch out to verify...just to test while you are there...it is a safety and cant be left like that...or just get a new pressure switch...you sound pretty handy ...if you have a multimeter you can test that switch to see if it opens and closes...(remove wires and jumper together) while testing multiple times...thats how you catch em dirty

 

[naturalgas]

Checking the vacuum port on the inducer motor was the first thing I tried. Port was not plugged and hose is in good condition and on tight.

Gas pressure is good cause my furnace runs great. How do I vacuum test the vaccum switch? I do have Mityvac pump kit, would that work?

Magnetometer to check if inducer motor is getting up to speed and pulling enough vacuum.But simple way to check is watch the little ball that pushes on the micro switch when the inducer motor starts you can see it move, very easy. I would take a tiny screw driver to make sure it was moving all the way to make switch. Try to check in fail condition , if your getting 24volts at module, it's the module


Sent from my iPad using Tapatalk

 

[naturalgas]

Pressure switches very seldom fail, they are simple devices. In 36 yrs I probably replaced a handful, mostly because of condensate back up and corrosion


Sent from my iPad using Tapatalk

 

[Never Too Old To Learn]

Do not use mityvac,you will damage the va. switch.I use a dwyer gauge capable of positive and negative pressure,I do not know how to post pictures,Checking continuity while inducer is running is a good idea.If no continuity remove inducer assembly,sometimes the orfice behind assembly rots,causing lack of vacuum,use orange high temp. rtv to reseal the inducer assembly.good luck

 

[pawel]

I will do more testing tonight as suggested. Thank you for everyones help, I appreciate it.

 

[pawel]

UPDATE:

Changed the flame sensor/ignitor and it starts on the first try now. Tested the boiler 3 times tonight and it started each time. Final test will be tomorrow morning...

I noticed that with the old part it would only try to spark once, and on the new one, it ignites on the 2nd "spark".

Again, thanks for everyones help.

 

[bobbyjean]

good job....make up a service ticket and bill the customer
you can hang on to that old ignitor/electrode...nothing wrong with keeping a backup plan for a cold winter nite....

 

[Never Too Old To Learn]

My advice was based on you removing wire off the vac. switch then reinstalled it unit came on,glad you got it going should give you satisfaction,everyday is a possible learning expierence.