Very strange boiler problem

rc23

Okay so I noticed a couple of days ago that my gas boiler was acting strange.
I turned on the heat on my thermostat and my radiators were heating up. But after about 20 mintues the radiators weren't giving off heat when the thermostat was still calling for heat. I checked and saw the boiler vent damper was open and boiler temp. dropped to 105 F.

So then I turned the thermostat off and then back on to heat and the boiler started to fire up again. So i decided to observe the boiler to see what might be causing this issue.
1)First the boiler heats the water to 145 F.
2)Then the circulator pumps the water to the radiators and the temperature drops to 135 F and the boiler fires again at that time to bring the water to 155 F.
3)The boiler water is still circulating to radiators and the temperature went down to 135 F in around 15 minutes time and the boiler is supposed to fire up so the boiler damper started to open again but the boiler does not fire up(the thermostat was still calling for heat). Then the temperature started to drop fast and went down to 101 F. So I did the same thing immediately turned the thermostat off and on and the boiler fire again and then its the same thing with the vent dampers in the open position over again.

So basically when the thermostat is turned on and calls for heat the burners fire up and will keep firing up when temperatures drop but after a certain period of time ( not really sure the amount) while the thermostat is still calling for heat the dampers will open up but the boiler will not fire.


I have I upgraded the factory aquastat to a hydrostat 3200 plus but I noticed the TR and the TH terminals on the gas valve was switched around according to the wiring diagram. I corrected the wiring but still getting the same issue.

So I tried different things:
1) Turned the burner power off and on still same issue.
2) The hydrostat is set to economy mode 4 so I tried to turn off the economy setting when the dampers were in the open position again and voila the burner started to fire up again.
3) checked the roll out switch and high limit no problems
4) checked the voltage reading on the burner circuit when firing on it was 24v and when the vents were open but doesn't fire it reads 0.1V

So what are you guys opinion? Im thinking it might be a defective hydrostat. Are these devices prone to these failures on what seems to be a pretty simple operation. I would think there would be some kind of fail indication but nothing at all.



This is a dunkirk pvwb-5d boiler with 2 zone valves
Gas burner valve Honeywell VR8200A 2264
Upgraded to hydrostat 3200 plus turned on economy mode

Steamhead

I'd bet the vent damper motor is going bad. What model is it?

rc23

You think so? Vent damper motor seems to operate without issues but could the terminals on it be going bad cause of the initial incorrect wiring on the gas valve? Also is a effikal rvgp-ks-6bkf damper.

AMservices

What is the high limit and differential set to?
With the temperature jumping around like that, I'd say bad control.
You said the when starting the heat the boiler will heat heat the water to 145° before the circulator turns on. are you sure about that?
Circulators should always be running during a call for heat.

lchmb

does it run to satisfaction with the economy mode shut off? The hold off on the circulator is because of the control feature... feature 5 is turned on. When you have 2 zone's the recommended setting of the economy feature is 2..not 4... I would shut it off..try a couple cycles..if they seem good set it to 1..see if it heats the house..if it does with no issue's move it to 2...try that for a while.. btw not sure that boiler wants the circulator held off....may want to read through the boiler manual

Paul48

Make sure you read and understand the info about economy mode. I'm not saying it's right or wrong, but maybe they address this condition in their literature?

Paul48

@AMservices
Again....I'm not sure, but it could have a feature to prevent condensation and hold the circ out.

HVACNUT

When the Hydrostat is in economy mode (4 is pretty high), the boiler temp limit will fluctuate according to the temp of the return water.
But if the damper is opening, then there's a heat demand. Might be a bad end switch in the damper.
There should be a switch on the damper motor. While the damper is open, switch it to manual open. If the burners fire up, it's a bad end switch and you need a new damper/motor assembly.

Paul48

Is the vent damper plugged into the hydrostat?

rc23

Okay so I just turned the heat back on and this time the boiler didn't fire. I went and took a closer look at the vent damper as some of you mentioned. The little pin sticking out on the side where the open/close is didn't look like it aligned with the marking so I gave it the lightest turn to the left and the burner kicked in. But now im not sure if its something that is stuck in the vent that is causing the problem cause as far as i can tell the damper opens and closes every time.

Steamhead

It's the damper motor. The end switch is going bad. Field Controls acquired the Effikal line a few years ago- the replacement part # is GVD-RMA. Have a pro install it, to avoid an unsafe condition.

HVACNUT

Until it's replaced, put the switch in the manual position.

brownman78

I have the same type problem and I noticed it on the coldest day about 10 degrees outside about a week after I had a new Columbia boiler installed with a Hydrostat 3200 Plus installed on the boiler.
This is my sequence of failure.
1. Call for heat
2. damper opens, pilot lights, and burner turns on, blue light on Hydrostat turns on water heats up to 125 degrees, circulator pump turns on.
3. water cools down to about 115 degrees, pump turns off, burner still firing. water heats up to 125degrees circulator pumps turns back on and stays on until the water temp reaches 145 degrees.
4. When the water reaches 145 degrees the burner turns off the damper closes and the circulator pump continues to run, and the water cools down to 135 degrees.
5. After the water temp reaches 135 degrees, the damper opens (this is the problem) The pilot lights for about 1/10 of a second give or take, and everything shuts down, all lights on the Hydrostat turns on (ALL LIGHTS), then lights 1 Temp Active, 3 LWCO, and 4 LOW WATER and 5 Economy Active stays on, the others turn off, then the Low water light turns off and the circulator pump turns back on, damper closes and reopens and the sequence repeat itself. sometimes this will repeat up to 10 times before the burner fires and stays on and the unit will function properly, heating the water up the 180 degrees in stages without a hiccup. Sometimes it will heat to a temp over 145, 155, 165, 175 and so on) but whatever temp it reaches, if it acts up the circulator pump runs until it reaches 135 degrees before the damper reopens or the burner tries to fire. When it's very cold out, I have to turn the hydrostat to off, and it will reach the high temp, it may still repeat the failure, except it will continue to try to fire the burner until it lights.

Steamhead

Try switching the damper motor to its manual "Hold Open" mode. If that solves the problem, replace the motor.

mattmia2

You can reproduce it, trace through the safeties/controls with a voltmeter and see which one is open. Should be 0vac across it when it is closed, if it is 24vac it isn't closing reliably or is not closing because it is doing its job as a safety. Finding it will tell you what to do next.

mattmia2

@brownman78 you should start another thread about this, i was answering the original question, yours sound like the control is losing power for some reason. that could be because of the way the safety chain is wired or it could be some other reason.

HomerJSmith

This relay fails intermittently. It is 2 pole-one pole turns on the circulator the other pole turns on the safety circuit and the gas valve. How old is your boiler? If it is old, I think that the back of the circuit board where the relay attaches to the circuit board there is a solder break in the connection. This is often intermittent and the result of the vibration of the relay closing, stressing the solder joint.
One can remove the circuit board out of the housing and examine the relay for a crack in the solder joint. You can re-solder the relay connections and place the aquastat back in service. Be aware that there are 110 V and 24 volts that are protected from each other by insulation paper. Make sure that the capillary tube that goes into the boiler well doesn't touch the 110 Volt circuitry-or ZAP!

OR...you can buy a new aquastat.
Jumping T and TV on the aquastat will turn on the boiler, do you still have the failure. Pushing down on the relay bar when there isn't a call for heat should turn on the pump and fire the boiler.