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MGREEN
02-18-2008, 10:45 PM
My home heating system is an oil fired, forced hot water, baseboard type.
About a week ago, it was very cold and with the thermostat set
at 70 degrees, the room temp was struggling to get past 60.

The furnace would run for a few minutes and then kick off for
a little while and then repeat this cycle.
We had this behavior in the past to the point that it would
just stop running.
So a call to the fuel co. for a service and cleaning and maybe
a filter change, and we would be back in business.

This time around the service guy checked the system, and said
that everything seemed to be in order, and that due to the cold snap
we were having, that the system was having a hard time keeping up.
The water temp was set to 180 degrees and when the water temp dropped to 140 degrees the furnace would fire again, and cycle like this
as it needed to.
So he said that all that he could really do would be to set the
water temp up to 200 degrees and so he did.
That was at about 8:30AM.
The room temp got to 70 degrees at about 2:30 in the afternoon.
Everything seemed fine until this morning when the furnace kicked on
and the water in the pipes started to sort of gurgle for a little while
and then would quite down.
We turned the heat off this morning, as it was near 50 degrees outside today, and turned it back on in the evening.
When it got turned back on, it started making the gurgling again
and then got quite again as before.
I've never heard the system do this before in the 10 years
that we have been here.
I dont get what's happening with the system.
The only change is the 200 degree water temp.
It sounds like there is air in the system, but I have no
clue how it got there? Or if it is indicitave of a problem.
Anyone care to hazard a guess?
Mike Green

Oldbrock
02-19-2008, 12:27 AM
It depends where the temperature control sensor is. If it any distance at all from the heat source the region being directly heated is probably reaching boiling temp and you are getting steam in the lines. Only my guess.Peter ( not my field but this came to mind )

Bruce Griffing
02-19-2008, 03:00 AM
Hot water systems have something called an air scoop. The air scoop sits at a local high point near the furnace and removes air from the water. I suspect you have air in your water. This will place a significant limit on you heating capacity. This may not be the correct answer, but I would start there.

ptjw7uk
02-19-2008, 04:50 AM
Did the engineer check the water pump, is it gurgleing or kettling.
Kettling occurs when the water in the system is not being circulated fast enough and you end up eith water trying to boil in the bolier.
Just a thought.
Peter

Your Old Dog
02-19-2008, 05:11 AM
Our water system was so quiet you couldn't hear the pump running. You sure it is running? And what Bruce says about checking for air in the line. My system had this little bleeder valves on one end of each room. I had to put down a cookie sheet and open the valve with a wrench and screwdriver until the water came out in a steady stream to let out the air. Look for a nut with a slotted screw head in the top, that would be the bleeder valve. Had to do mine every 2-3 years.

Bruce Griffing
02-19-2008, 05:28 AM
FYI, here is an air scoop:

http://www.amazon.com/Watts-Brass-Tubular-AS-M1-Boiler/dp/B000KL7TE4

SGW
02-19-2008, 07:30 AM
I think I'd check for air in the system. Do you have bleed valves on the baseboards? Take off the end covers and look for a little valve with a screw slot to open and close it. Open one up (with a cup under it to catch any water) and see if you get air coming out.

Ken_Shea
02-19-2008, 07:37 AM
To add to the suggestions,
Had a similar problem a few years ago, the pump impeller/ anti toque coupling was slipping on the shaft, two set screws on this system, tightened it up and that took care of the problem. What it was doing was slipping/catching during on and off cycles.


Ken

JCHannum
02-19-2008, 07:50 AM
Ditto bleeding the system to start with. Each radiator or heating section has a bleed valve, bleed them all.

If it is cycling on and off, it is one of the safety limits, not the temperature. If it could not keep up, it would run continuously.

Make sure there is enough water in the boiler, there should be a compound gauge for temp & pressure, or individual gauges. Pressure should be around 10-20PSI when not firing & around 30PSI when firing.

If the circulator pump is not working, or a squirrel is stuck in the stack, high water temp or high stack temperature limits will cause it to cycle like that.

If the expansion tank also might cause cycling if it has lost it's charge, and make it go off on high pressure. Watch the compound gauge while it is running to see what is happening when it cuts out.

meho
02-19-2008, 08:43 AM
Lots of good info here. I would add that you need to check the water fill regulator/valve strainer. The bottom of the regulator should unscrew and there is screen in there. They become clogged and need to be cleaned. I clean them yearly.

Air in the system and or lack of water flow are most likely the culprets. If the water boiler is making steam you should know it. It will trip the pop-off valve, make a lot of noise and belch steam out.

Sparky_NY
02-19-2008, 09:34 AM
Ditto bleeding the system to start with. Each radiator or heating section has a bleed valve, bleed them all.

If it is cycling on and off, it is one of the safety limits, not the temperature. If it could not keep up, it would run continuously.

Make sure there is enough water in the boiler, there should be a compound gauge for temp & pressure, or individual gauges. Pressure should be around 10-20PSI when not firing & around 30PSI when firing.

If the circulator pump is not working, or a squirrel is stuck in the stack, high water temp or high stack temperature limits will cause it to cycle like that.

If the expansion tank also might cause cycling if it has lost it's charge, and make it go off on high pressure. Watch the compound gauge while it is running to see what is happening when it cuts out.

Being in the heating business and having worked on a lot of boilers, the quoted reply above is the most accurate reply I seen.

As many mentioned... air in the lines.... thats what causes the gurgling noise, its a common issue. You don't know if the serviceman drained any water when working on it and then refilled it, if he did that will cause air to appear for a while. Freshly filled systems develop air until they have been bled of that air a few times.

There should be bleeders on the elbows at high spots, commonly under the corner cover of a baseboard. You will need a special square key to open the bleeders. Many hardware stores will have these keys.

Considering the system is cycling on and off, its not matter of the cold weather and the system not keeping up, if it was the boiler would run pretty continious. If its cycling on and off then check your baseboards to make sure the louvers are open on each one, and there is no obstructions at the gaps on the bottom. Air must flow freely through the baseboard for it to give off heat. (seen many times where people had new carpeting installed that restricted the gap under the baseboards and pretty much shut the heat off, had to raise each baseboard up about a inch to cure)

By the way, bleeding the air has to be done when the system is running and water circulating, turn the thermostat way up while you are doing the bleeding, then lower it when done to make sure its circulating.

wmgeorge
02-19-2008, 06:29 PM
Ditto bleeding the system to start with. Each radiator or heating section has a bleed valve, bleed them all.

If it is cycling on and off, it is one of the safety limits, not the temperature. If it could not keep up, it would run continuously.

Make sure there is enough water in the boiler, there should be a compound gauge for temp & pressure, or individual gauges. Pressure should be around 10-20PSI when not firing & around 30PSI when firing.

If the circulator pump is not working, or a squirrel is stuck in the stack, high water temp or high stack temperature limits will cause it to cycle like that.

If the expansion tank also might cause cycling if it has lost it's charge, and make it go off on high pressure. Watch the compound gauge while it is running to see what is happening when it cuts out.

I'd make sure there was water in the system or is it losing water?? The pressure on the gauge, IF the gauge is correct only needs to be equal to the height of the highest radiator to be supplied with water above the boiler in Feet X .433 this gives you the needed cold fill pressure. If the pressure is too high then the pressure relief on on the boiler might blow. Most water boilers are rated at maximum of 30 PSI, check the nameplate to be sure.

Has the boiler heated the house in the past?? If so I'd do like the others have suggested.... vent out the air. BTW pump / motor couplings can and will fail, in that case you'd have little or no circulation of water and the boiler would tend to short cycle and not heat the house. BG in Iowa

glenj
02-19-2008, 07:11 PM
I have an old oil burner and big cast iron radiators. I found I had to bleed them often, especially on the second floor. I could not find a leak anywhere. It turns out the pressure setting was too low. The pressure was not enough to keep the top of the upstairs rads above zero. This caused dissolved gases to come out of the water and fill the top of the rads. I upped the pressure 5 psi and now only bleed once in the fall at start-up and it hardly needs it. It won't help your cycling issue but it will with the air in the system.

RKNIT
02-19-2008, 08:14 PM
Check the circulator pump. I've put 2 "cartridge" type pumps in my setup in 2 years. They failed by getting hard to turn and stalling. (the [Green approximately 2.7" dia by 3.5" length] motor got hot enough to burn you.) No circulation and boiling noises in the boiler. Also, the furnace couldn't keep up with the need for heat. My house is tiny, so that was the giveaway. I replaced the cheap Green circulator pump with a Red {Bell and Cossette???} (I can't remember the makes of either pump. Sorry) cast iron pump with a separate motor. NOW the house heats from about 40 degrees to about 65 in an hour or so.
good luck.
Ron

rhmalsch
02-19-2008, 08:19 PM
If the system was sized correctly when installed and worked ok before this something else is wrong. A little close observation should reveal cause of short cycling. The boiler should fire almost continuously until thermostat is satisfied. Which control is causing the short cycling? Thermostat-adjust heat anticipator or replace thermostat. You can check by jumping out thermostat. High temperature limit- boiler is too large or not enough flow. Most systems are designed around 20 degree drop, 180 out 160 in at boiler. If temperature drop is greater flow is lacking. Broken spring coupler on pump is a common problem. Pump motor runs but pump does not turn. You will have some gravity circulation but firing stops on high limit. Cartridge type pump(Grundfoss) can have failed capacitor or trash in pump. If system pressure is ok noise in piping is air. Bleed air from radiation. If system has air scoop air separator make sure auto air vent on top is working. Cap on top should be loose until air is removed. Design fill pressure is 12 psi, enough for 3 story building. If pressure when hot is higher than 25 psi there is a problem with expansion/compression tank. Bladder in tank may have ruptured or lost air charge. Bladder pressure should be same as fill pressure(12psi)before system is filled. If open expansion tank it may be waterlogged. Drain and refill tank to restore air cushion at top of tank. Oil burners sometimes have enough bearing wear that rotor starts dragging and motor trips on internal overload. Motor cools off and restarts. Make sure to remove any jumpers installed for diagnostic purpose.