My two-year old Slantfin Boiler won't heat the house above 65 degrees, and it's
usually at 60 degrees. It'll come on and off randomly for short periods of time
(as short as one second) and over a long period of time, it may bring up the
temp to 65. As another example, I had the (new) thermostat, which my oil
company replaced saying that was the problem, up to 72 overnight and into the
day, and the temp in the house is still 60 degrees. I have also left the
thermostat pegged on high for two days with the same result. The company who
installed the boiler doesn't, for some reason, believe that this problem exists,
because when they came, the house was "warm" i.e. 65 degrees! and the gauges on
the boiler were up to the correct pressure. I have obviously severed business
relations with them, but I still have the problem. Any ideas what might be
I assume this is a hot water / radiator heating system (something
utterly unfamiliar to me, as all I've ever known is forced air natural
I would assume that the efficiency of your radiators are the problem,
and that measuring the temperature difference of the pipes that enter
and exit each radiator will tell you just how much heat that each one is
dumping into the surrounding air.
Assuming that the temperature of the pipes that enter the radiators is
high enough (I have no idea what that temperature should be - probably
150 degrees, certainly higher than 100) then I suggest you have a few
small fans blow air across each radiator to increase heat transfer into
the surrounding air.
Well, when the heat is on, they are quite hot all over. The problem is getting
the boiler to go on and run for a long enough period to heat. I just sat here
very chilly for about two hours - the boiler went on for a second or two twice.
Now it is beginning to kick in, but it still only stays on for maybe 20-30
seconds. Sometimes it does run for 15 minutes, but not usually.
Maybe you need to clean or replace the flame Sensor and/or logic card.
Newer units usually have a trouble light on the control card that gives
a blink code.
I doubt that anyone installed a unit that was too small for the building.
Then again maybe it just doesn't like you! ;-p
It is hardly too strong to say that the Constitution was made to guard
the people against the dangers of good intentions. There are men in all
Sounds like you've got a modern, "high efficency", unit. Among
other features, these measure the outdoor temperature
and compare it to indoors, and adjust the flame size
(and plenty of other things).
We had a similar situation with a different brand, and
it turned out to be a mis-setting of the outdoor sensor.
This was a new installation by the local Licensed, Insured,
and Professional HVAC rep, so he had missed it.
When he came by he scratched his head, then called
the distributer, who didn't even have to listen
to the whole speach, but told him right away what
Once he knew what to do it was just a couple of minutes
Knowledge may be power, but communications is the key
Any chance that if people like me reply to your post that you will follow up
with more information etc?
Did they just replace the boiler 2 years ago, or is it a whole new heating
system including the radiators etc. that were put in?
If they just replaced the boiler, do you know what the BTU rating of the old
boiler was? What is the BTU rating of the new boiler?
If they also put in all of the piping etc. do you know if it a 1-pipe series
system, a 2-pipe reverse return system, etc? Is the whole house cold or
just the parts of the house that are farther from the boiler?
Were you in the house prior to 2 years ago? If so, was it warm then.
How big in the house, what style (1-floor, 2-floor, ranch, cape cod, etc),
My old boiler was ancient - 50 year old, big. Then it puffed back and wrecked my
house. Anyway, I only replaced the boiler and the pipes leading into it. It
used to work fine (the new one). Although my ex-boiler guy insisted that the on
and off operation is normal, I really think it's important. I would say the btu
rating is less for the new boiler, but I don't know and I don't know what the
old one was. I've lived here for 13 years and it is a tiny house - 810 sq.ft.
one floor. Mostly new windows and insulation. The whole house is cold and I have
no idea about the piping. The weird thing is that it got my house up to 70
yesterday, for the first time in a long while. Today, it won't get going.
Thanks. That helps a lot. Now that it is clear that this new heater used
to work fine, but now is having a major problem getting the house to heat
up, that eliminates issues such as poor heater design, inadequate BTU's in
the "new" heater, etc.
Unfortunately, I don't know enough about heaters to be able to say what the
specific problem is or could be, but maybe others here do now that they have
The heater coming on and off is called "short-cycling", I think. A good
HVAC person should be able to figure out why your specific unit is doing
that. I know that there can be different kinds of controls or settings that
can cause that, but I can't say which one is causing the short cycling
problem. I know there are flame roll-out sensors etc. that can be a cause
of this type of problems.
I have an oil-fired hot air furnace (I know, that's way different than what
you have). It was doing the short-cycling routine. In my case, the heater
person came out and found a couple of problems. One was dirt and crud in
the chimney flue/vent. That set off some kind of sensor so that soon after
the heater started running it would shut itself off. The guy also said that
my air intake low temperature setting was adjusted incorrectly, so that
meant that the intake air was too cold and that would shut off the heater --
or something light that. Overall, it does sound like some sensor or safety
setting is doing its job and shutting down the heater soon after it starts
up because it detects a problem. Then the heater starts up again and the
whole cycle happens over and over again, which prevents the heater from ever
really getting to run a full heating cycle as it should.
Good luck. Sorry I couldn't offer anything more specific. If you do get
someone to figure it out, post back here what it turned out to be.
As I've been "adjusting" my 35+ year-old furnaces (both at home, and at
a small commercial office building) for the past 5 to 10 years, one
thing is clear to me:
Furnaces are horribly over-spec'd when it comes to their btu output
compared to the heat-loss the structure is experiencing - even on the
coldest, windiest days.
My furnaces are single-stage, non-condensing, constant pilot light, no
electronics in the furnace - but I do have fully electronic thermostats
The gas valves inside these furnaces have dial controls - one position
to start the pilot, the other (when rotated about 90 degrees) to allow
full gas flow through to the burners. These are furnaces that date to
the 1970's. (By the early 1980's, furnaces with electronic ignition
Instead of setting the valves to the full "ON" position, I set them to
maybe 20 degrees where I get a stable, SLOW flame on the burners. This
is like setting your barbeque gas setting to "low". The result - the
furnace runs longer, the heat output at the registers is luke warm, and
the temperature inside the structure is very stable and constant. Even
when the daytime temp's are only hitting maybe 5 to 10 f (as they have
been the past few days) and night time temps are 0 to -5 f.
Having the fan always running adds another "layer" of consistency.
The analogy with a boiler system would be to always be circulating the
water, and setting the gas valve on the boiler so as to generate the
minimal BTU output as possible.
The most efficient state for a furnace to be in is when it is generating
just enough heat to match the heat loss of the structure, and thereby
maintaining a constant internal temperature. In this state, the furnace
will always be generating heat, and that heat will constantly be in
motion, constantly being delivered into the internal living space of the
Modern furnaces that are set to come on at full BTU strength when heat
is called for is about as far away from this ideal, efficient state as
you can get, as the thermostat or other sensor/control systems struggle
to cope with the feedback effects and overshoot / undershoot of the
desired set-point temperature.
Modern furnace multi-stage with AI based electronic thermostat generally
does a good job. If valve opening is arbitrarily adjusted
it is messing with original design spec. When system is installed
without proper calculation it creates all kind of comfort and
efficiency problem. You are talking about old furnace which nowadays
can't even be installed legally any more. I am in Canada. In my house
temp. over/undershoot is less than half deg. Celcius which no one even
Short cycling means either system is too big or some thing is wrong
specially when temp. setting is not met. I am retired from Honeywell
after almost half a century, LOL! I lived thru evolution of technology.
From mechanical relay logic to ASIC based electronics control and beyond.
Hmmm....hot water or steam. I think hot water - I have radiators, with water
pipes plumbed into them. Someone recently said steam, but I think that was
wrong. I think they are filled with water. I think this is true because when I
had the house remodeled when I moved in, the shaky contractor disconnected one
of the radiators and flooded my living room. I can also hear water glugging
through them a bit sometimes when the heat first comes on. Not a steam sound.
"Pegged on high" mean turning the thermostat all the way up and leaving it there.
And BTW I REALLY appreciate everyone's responses. It seems like a sensor problem
- that something is tripping it. But let me be clear - I am an idiot about these
In many areas, including I'll bet, furnaces, it's not possible anymore
to buy something that is really simple. Even the cheapest cars have
airbags, etc. for example. So I wouldn't be surprised if you do have
the sensor he refers to.
Did't they give you an owner's manual for the furnace? I read mine
cover to cover. I didn't understand everything the first couple times
but over the years most of it became clear. (or course my oil-fueled
forced air furnace is 35 years old.) There will certainly be a
reference, if only in the wiring schematic, to outside sensors, although
conceivably even then they may be optional.
What make and model number is your furnace? Maybe someone here will
find the manual online. But you should still read it yourself. Maybe
it's hanging from the boiler?
I never even got to really understand all of the workings of older model
heater units. Newer heaters are even more complicated with computerized
The one thing that someone mentioned about the newer models is that they
typically have a small red signal light that is either always on or blinks
in a pattern. I have a few of those. There is usually a little peep hole
that you look into to see the signal light. The light pattern -- such as 3
short blinks in a row or whatever -- is supposed to indicate what the
problem may be. And, most of these have instructions right there on the
heater that says what each pattern means. Try looking for that.
I live in an area where our natural gas supply company (PSE&G in my area)
will come out and look at my heater for free if it is not working properly.
They can usually then tell me what is wrong with the heater and tell me how
much it would cost for them to fix it. Their repair prices are usually
higher than normal, but if I decide that I don't want them to do the repair,
there is no charge for the visit. Maybe if you post the name of the natural
gas supplier in your area someone here could tell you if they have that free
check policy. Or, you could call them and ask them. In my area, the PSE&G
repair technicians really are experts at what they do. I have never had
them come out and not be able to tell me within about 15 minutes what the
problem is and what needs to be done to fix it.
So, it is a free diagnosis. I often then just have them do the repair, but
sometimes with my hot water baseboard/radiator heat systems similar to yours
they may say that it is a bad circulator pump. And, they will tell me "off
the record" that if I know how to change the circulator pump (which I do,
and it is easy), or I know someone who does, I could do it for a lot less
than they would charge. That's because they also have to charge to drain
and refill the heating system (which isn't really necessary) when they
change the circulator pump. Then I thank them, they leave and there is no
charge, and I fix it myself or have a handyman person that I know change the
circulator pump (the circulator pump costs about $75 at Home Depot -- called
a Taco circulator pump, I think; and it takes about an hour max to change
the circulator pump).
I own or have responsibility to manage about 12 different dwelling units
with different types of heaters and HVAC units which is how I learned some
of the ways to solve heating problems at various times -- sometimes on my
own, and sometimes with the right people coming in to diagnose and/or fix
My bet is that your issue is an easy fix if the right person looks at it for
Let us know what it turns out to be. Feedback like that, here and
elsewhere, is how I learn about a lot of these issues.
In case it helps, I decided to try also posting your question on the
alt.home.repair newsgroup which tends to have more people who are active
there and may be able to post ideas or suggestions. Check there --
alt.home.repair -- if you want to follow-up in that group.
You really should get this straight.
Last I checked, if it's hot water, there is a pipe at each end, and a
small spigot at the top at one end, with a square peg inside of it,
that you can and probably should buy a tool for, to bleed the air out of
the radiators, so they will work right. If a radiator is warm or hot
to the touch towards the bottom and as you rub your hand up, it suddenly
is quite a bit less hot, you have air in the radiator, which will lessen
how well it works. That's not the problem you posted about however.
IIRC many people bleed their hot water radiators every year when they
start using heat.
If it's a steam radiator last I looked it has only one pipe. (When the
steam cools and turns to water, it runs down the bottom of the same pipe
the steam is in.) and it has a pressure release valve which is a little
bigger than a large spool of thread (if you've ever seen a large spool),
with a dome on top, often chrome, and maybe sometimes steam will come
out, but my bed was right next to one for 10 years, and iirc it went up
to 5 years without any steam coming out.
As I'm telling my friend whose about 60 and has lived in an apartment
all his life, but plans to buy a house, if you're going to have a house,
you have to know this stuff.
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