I have a 10 year old forced hot water heating system. 3 zones-- main floor, upstairs and hot water. The furnace comes on and runs for only about 3 minutes. It does this about every 30 minutes. Sometimes it shuts off and the boiler temp reads 160,and sometimes it shuts off at 190. The system seems to be working properly for hot water and upstairs. We have replaced the zone valve head, the cirulator, the aquastat, tired 3 different room thermostats and run new thermostat wire. The tech came out and tested everything --said all the zone valves are reading right where they should be and that the ciruclator was bad (no doubt it was--bearing were just about gone). He made a few adjustments and when he left it was running fine. One cycle. Seems like if you turn the thermostat up it will run correctly for one cycle then it messes up again. I keep reading about how a dirty boiler can cause this. Is this true? We had a regular yearly maintenance service done about amonth ago, but the guy did not take the boiler apart and clean the radiatorlike part inside. I can't afford to keep replaceing parts and having the furnace still screwed up. Any suggestions will be helpful

I do not think you have a problem. Your system is designed to keep the water temperature in the boiler between 160/190 no matter if there is a call for heat or not. If your control was tighter it would cycle more often and that would really drive you nuts.

Unless you have real hard water or your boiler is using a lot of make up water scale (that is what it is called) should not be a problem.

Then can you explain to me why the temperature in the boiler drops so quickly that the furnace has to come on every 10 minutes even when it's not calling for heat----and why the heating baseboards aren't getting as hot as they used to---more like pea warm? And why once it runs through a acycle or at the most 2, the room temp can drop and sometimes it won't come back on unless you crank the thermostat? And why it's sometimes only staying on for about 30 seconds? It's never come on this often even in the middle of the winter and now it is? Came on at 8:58 shut off at 8:59. Came back on at 9:08 went off at 9:10. Sometimes the water temp in the boiler only drops to 180 before it comes back on and sometimes it drops to 150. The furance tech that replaced the circulator told us that the normal cycle is for it to come on and run for 10-15 minutes (unless the boiler reaches its maxsafety temp and it will shut down until the water cools down and then cycleagain until theroom temp is reached). Now it can be cooled down to 160 and be back up to shut off at 190 in less than 3 minutes? And going through oil at a 1/4 tank a week when its 60 degrees outside? That just doesn't make any sense to me--- especially when I have listened to this unit run for 10 years and it's never come on this often.

Also, why would it come on to maintain the boiler water temp when it's only dropped to 180 sometimes, and other times it's circulating the water when it's shut off and the water is only at 150? Every time we let it run on it's own the cycle time continues to get shorter. I still don't understand if it's all to do with maintaing the boiler water temp rather it calls for heat or not --why doesn't it do the same thing in the summer-- we never changed anything for the summer except we turn the thermostats down so the furnace won't compete with the air conditioner

And why would the furnace have stayed off now for a full 20 minutes even after a 10minute hot shower---and have come on every 10 before and not even gotten the baseboards hot? There is no consistancy to it.

If you have a boiler water leak that could cause the boiler to run motor often and run when there is no call for heat. The system requires that the boiler maintain about 12 lbs pressure and you probably have a automatic fill valve that keeps adding water as it is leaking out. Naturally this is a complete guess on my part but I have seen this before. It would also explain the excessive oil consumption since the boiler has to keep heating the cold water being added all the time.

You are asking a lot of questions that cannot be answered here since I cannot see or test your boiler system. The professional that was there should have picked up on all your complaints but since he did not check the water leak situation. Now a water leak might not be a easy visual one. Could be some of the pipes are hidden or the safety pop off valve is leaking down the drain.

There is no drain--it's a dirt cellar. The one thing I don't think I mentioned is that we have a 50 gallon hot water storage tank. Could the system be running as if there isn't one? Right now it's been off for over 30minutes after running forjust 2minutes and the long andshort ofitis, there is no consitancy to how it's running

I am all out of ideas and guess work at this point. My suggestion is to contact a professional in your area for a on site inspection of your entire system. You said that a tech was there and said all was OK but obviously in your opinion it is not. Could be a different contractor might see your situation in a different light and find a problem.

The first test I would do is a pressure test of the water system the on to the controls/thermostats for accuracy IE heat anticipator settings/adjustments.

I have nothing left to offer since I cannot see or test your system from here. Good luck.

Thank you. I told my husband what you said about the furnace coming on continuously to keep the boiler water from dropping below 160. He said that would sound fine if it wasn't for the fact that the furnace came on only twice today and the boiler water is currently down to 100. The only thing he did was turn the hot water storage tank down from 135 to 120. We still have hot water so it hasn't gotten cold without the furnace running every 10 mintes

Here's a reach... what type of valves are on the system? I have seen plenty of old gate-style valves fail because the gate or stem stripped. The valve handle can be turned until it stops but the gate does not move. This would only apply if the problem surfaced after any valves had been operated. And, if you have any valves of this type. If so, try this: turn the valve handle to the approximate mid-position. BE VEWY QUIET and twist the valve handle back and forth. If the stem and gate are still intact, you should hear a faint sound of the gate against the valve body.

Not sure exactly what you mean,but the zone valves or the "head" I think they call them--has a lever that moves up or down--- the up position is automatic and the down position is manuel. Yesterday it was quite warm outside (70) and the unit came on a couple of times throughout the day --- 6 hours or more apart---and ran for about 3 minutes. It came on once and ran for 10. The boiler water temp read 100 at the coldest and 180 at the hottest. Sometimes it only drops to 160 and comes on and shuts off at 190. It came on at 4am andran 3 minutes and stayed off until 8 am and ran 3 minutes. The furnace in in thebasement under my bedroom so I know every time it comes off and on during the night. It has not come on since 8am (it's now 9:58), and we have run the dishwasher and filled the rug shampooer several times and used the shower. The thing that is frustrating me so much is that when I say it's coming on every 10 minutes and running for 2 or3 then shutting off anddoing this cycle repeatedly, Iget told that it's normal and the unit iscomingonto maintian the boiler water temp between 160 and 190 (yet sometimes the water has droppe down to 100-130), and when I say now it's running for 10 minutes or so and shutting off for several hours until the room temp drops below the thermostat setting or we turn the thermostat up, I get told that's normal--- Can someone explain to me how the same unit running 2 totally DIFFERENT ways, with no consistantcy can be normal? How can it supposed to run so the water temp in the boiler doesn't drop below 160 and yet also supposed to shut off for hours and let the water temp drop below 130? (by the way,I've listened to this unit run for 10 years and the run for 20 minutes or so when calling for heat for a room and then stay off for a longtime until the room calls for heat again is how it's always been until last year when it screwed up and started cyclingon andoff literally every 30 seconds---ended up having to change a thermostat and it solved it), and it had never run a 10 minute cycle in the summer when we still have it on for hot water)Ijsut wish Icould get a straight answer as to why it's not running consitantlay one way or the other

Ijsut wish Icould get a straight answer as to why it's not running consitantlay one way or the other

In order to get a strait answer a visit to your home by a professional will be necessary. Now I said a real professional who has the proper testing equipment like a chart recorder to test your unit over a period and events.Testing needs to be done and a complete control system check needs to be performed. It is possible the main boiler temperature control is out of calibration causing the wide swings in the temperatures you are complaining about but all ideas give here are just good guesswork on our part since we cannot actually perform tests to come to a logical conclusion.

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Perhaps I wasn't clear enough. The zone valves control flow to supply heat where needed. The valves I was referring to are generally provided for service, to isolate a portion of the system when necessary for repairs, etc. Your system may or may not be equipped with them. Like I said earlier, it's a reach. I have to agree with HVAC1000 regarding the prospect of a faulty temperature control. It would be the most likely cause of the erratic cycling patterns you have observed.