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Heath, HVAC Technician
Category: HVAC
Satisfied Customers: 1034
Experience:  11 yrs. comm.resid. service, Type III Cert.
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How to adjust water temperature on oil furnace?

Resolved Question:

How do I change the water temp on my furnace? Someone turned it down to 100 degrees.

Submitted: 6 years ago.
Category: HVAC
Expert:  Heath replied 6 years ago.

Heath :

Hello, It will be my pleasure to assist you. There should be a gray colored box inside this box is the temperature adjustment for the boiler. Once you have the cover off you will see a dial with temperature settings on it. Its usually to the left side middle of the box. Adjust it to 180. This is a good boiler set point.

JACUSTOMER-cdt8lso8- :

All I see is a temperature gauge on the outside of the furnace. I don't see any way to adjust it. Where would this box be located? This is an older furnace, probably from the 60's

Heath :

Its a boiler right?

JACUSTOMER-cdt8lso8- :

I'm not sure what that is? The model is Weil-McLain. I'm sure it's not made anymore! I can remove the front panel, but all I see is the motor

Heath :

Do you have a thermostat? This furnace blows hot air into the house or does it have radiators?

JACUSTOMER-cdt8lso8- :

Yes, Only one. Hot water radiators. I used to be able to take a 10-12 minute hot shower, now the water runs out after a few minutes and takes about 5 minutes to come back up. Ok in the summer but it's colder here now! i haven't yet turned on my heat

Heath, HVAC Technician
Category: HVAC
Satisfied Customers: 1034
Experience: 11 yrs. comm.resid. service, Type III Cert.
Heath and other HVAC Specialists are ready to help you
Expert:  Rick replied 6 years ago.

Welcome to Just Answer,
Since this an oil fired boiler it's possible the the hot water coil is clogging up with mineral deposits. Your describe classic symptoms of this problem. If this is the case turning up the boiler temp won't solve the problem. The fix is usually to flush the deposits out by pumping acid through the coil. This a not a DIY project.

Customer: replied 6 years ago.
The temp reads 100 degrees, this problem with running out of hot water didn't start until the temp was turned down. I need to turn it back up and need to know how without paying $100.00 for a service call if possible
Expert:  Rick replied 6 years ago.

If you are reading the temp on the gauge on the boiler you could be getting a false reading. These gauges are notorious for failing. If you want to try to turn the temp up, you need to locate the operating control. The control is probably a grey control box that is projecting from the hot water coil. Take the cover off (there may be a screw at the top and/or bottom), you should see 3 dials. Turn the one marked lo limit or lo(w) up to as high as 150. But like I said before I doubt this will solve the problem. It might but based on your description, I doubt it.

Customer: replied 6 years ago.
I cannot locate this box for the life of me, the furnace is old and the size of a small fridge, the only things that project are the temp gauge, the emergency reset and the on/off switch. I would at least like to try adjusting the temp before calling for service. How can I locate the control box?
Expert:  Rick replied 6 years ago.

If you post a (several perhaps) pic(s) here I could probably steer you in the right direction. I need a pic of anything on the boiler with wires coming out of it.

Here are instructions for posting pics

1.) If you see a tree icon in your tool bar at the top of the reply box ( where you are typing ) go to number 2 .

If you don't see one then press show tool bar on the upper left of the reply box and then go to number 2.

2.) Press the tree icon, you should get a window that has a browse button option on it.

3.) Press the browse button on this box. You should then get a second box with a browse button on it.

4.) Press the browse button in this second box and you should get a window that you can use to navigate to the location of the photo file on your computer.

5.) Make your choice of photo file by double clicking on it. The choice box should disappear and the path to the photo file should now appear in the box.

6.) Now press the OK button on that box. That box should disappear and the path name should show up in the first box now. If it doesn't show right away give at least one full minute.

Don't press the insert button until you see a path name in the box. It will only show up as a red x if you do.

7.) Press the insert button on that box once the file path appears.

Customer: replied 6 years ago.
Expert:  Rick replied 6 years ago.

Like I said before I doubt that turning up the boiler water temp will solve your problem since you describe classic symptoms for a hot water coil that is coated with mineral deposits. It's also possible that you have a tempering valve that is faulty. The tempering valve (if you have one, you should) mixes some cold water with the very hot water coming out of the coil so you don't get burned. It would be attached to the water lines connected to the coil. It would look something like this
Tampering valve
If this is an old valve it's probably seized up and you won't be able to move the dial. It may need to be repaired or replaced.

I can't help you find the operating control without pics. You could try adjusting the settings on your camera for a smaller file size (usually the email setting on most cameras).