Please help. Peerless Boiler short cycling

partlyleft

I have a natural gas Peerless cast-iron DE-06 that is short cycling. I'm getting ignition for less than 10 second intervals when call is sent from Stat.

When I cold started the unit after cleaning the Hx and Burner tubes the unit short cycled as well until set temp was reached albeit with slightly longer intervals.

The exhaust fan does not always turn off right away with the flame so I was hoping this would help me diagnose a bad Stat. The btu may be slightly oversized but given the extremely short cycles I think it's something else?

Could the flame sensor be to blame? Can it be cleaned or does it need replacement?

Big Ed_4

First check to make sure the pressure lines are breathing . The nipples screwed into the vent tend to plug...

partlyleft

Oh I'm sorry are you referring to steam, this is a water radiator system.

Big Ed_4

There is a pressure switch , it is used to prove to the control that the fan is doing its job . There should be two hoses that connect to the pressure switch and the flue hood . They should not be plugged ....

JUGHNE

Also, while doing your cleaning, you could have interrupted the return grounding path for the flame sensor.
Flame sensors need 2 conductive paths to work. One is an obvious wire and the other is a ground path thru the metal parts, sometimes there is an actual ground wire to assure the ground path.

Or you can clean the flame sensor rod with Stainless steel wool.
If this has a hot surface ignitor (glow stick for ignition) that also doubles as the flame sensor, those are fragile and you do not want to break it.

Post pictures of ignitor and flame sensor if possible.

HVACNUT

The main burners are only on for 10 seconds at a time?

partlyleft

Wow thanks all for the input, I'm going to try to respond to each as I get into. I've determined the short cycling is intermittent now, yes 10 seconds or less flame on main burners and fan seems to run what I'm guessing is an extended purge. 

But this isn't always the case. Sometimes flame on is far longer and seems normal as well for fan off. 

I think it is hot stick. Pictures coming soon. 

I cannot find the low limit boiler temperature switch even though manual states adjusting it. Diagrams only show the high limit.

partlyleft

JUGHNE said:

Also, while doing your cleaning, you could have interrupted the return grounding path for the flame sensor. Flame sensors need 2 conductive paths to work. One is an obvious wire and the other is a ground path thru the metal parts, sometimes there is an actual ground wire to assure the ground path. Or you can clean the flame sensor rod with Stainless steel wool. If this has a hot surface ignitor (glow stick for ignition) that also doubles as the flame sensor, those are fragile and you do not want to break it. Post pictures of ignitor and flame sensor if possible.

The grounding path I believe is through the pilot supply line. The pilot and flame sensor are attached to the center burner tube by a small set screw that barely has enough clearance to join the two before bottoming out.

Yes I was trying to find the ignitor part replacement to no avail in the manual before I would think of touching it. 

partlyleft

HVACNUT

@Big Ed_4 might be on it. If the fan stays on but there's flame loss, 24 volts is lost to the ignition module. The 24 volts comes from B1, then through the pressure switch and the rollout.Unlikely the operating control losing B1, because then the fan would stop... unless there's post purge. Sorry, I'm not familiar with either of those controls. Read through the manual. 

Do you have the Beckett control? It shows a Boiler Ground Stud so I assume grounding is very important. Shut off the power and check all connections. 

partlyleft

Update: ignitor glows and pilot lights, 26v from controls good but burners will not light at all now! 32f out

partlyleft

I have Honeywell SV9601

partlyleft

I have less than a few ohms from that bracketed burner tube over to gas valve body

JUGHNE

Smart Valve??? I thought that pilot assembly looked familiar.

If it is smart valve, the hot surface ignitor (HSI) has the 2 blue wires going to it. I don't recall if separate flame sensor or not, but see another wire with the blue wires.

HSI is very fragile. IIRC, that entire assembly can be replaced as one unit.

JUGHNE

Looking at that assembly lying on my desk.

Has a tiny HSI that runs on 24 volts, a flame sensor rod with a slight bend in it....all one unit.

It is a Honeywell A3400A Igniter-Flame Rod Assembly.

It does state it will fit for the SV9601 and 7 others.

If you take the entire pilot out, there is a clip that holds the HSI/rod in place.

The pilot burner hood where the flame is is the "target" for the flame rod.

It must be clean as it is the conductor for the return signal. The flame rod is the other conductor.

Both must be shinny clean.

Usually just replace.]

Instruction page is HW 69-0751-05 if you want pictures.

JUGHNE

Smart Valves has the gas valve handle the ignition and flame sensing functions.

Some of the first ones were not very "Smart" and died within weeks.

They are difficult to trouble shoot also, so replacing the HSI/FS was the first thing.

As in many MoneyWell products, "you can buy better but you can't pay more"

EBEBRATT-Ed

The pilot flame in your last picture looks very yellow. The pilot assembly is probably dirty and the pilot is not getting air. Remove and clean it

partlyleft

Update, went back cleaned ground contact with screw and plate, I have burner flame!!

JUGHNE

You sir are lucky. Just go on line and price a new Smart valve and HSI which is what you might have gotten installed by an unknowing "Pro".

Then take everyone out to dinner! Merry Christmas!

partlyleft

Yes I called supply house they wanted almost 500 for the gas valve and 120 for ignitor pilot assembly which I was suspecting!

I have seen ground issues cause other electronics including automotive ECUs to stall vehicle, no start etc. I guess the ohm reading couldn't be trusted in terms of true ground signal strength.

Now boiler is heating up to limit without interruption!

Thank you all dearly,

Merry Christmas 🎄 🌲!