I have a situation in a Victorian home apt where one of the four radiators will not get hot. (The apt has its own boiler) The other 3 radiators in this apt work, in fact, one of the other radiators seems to heat excessively (in comparison to the thermostat setting). The non-working radiator gets luke warm after about 2 hours. It has been bled so air would not seem to be the problem on the surface and the boiler was professionally serviced not long ago. I am a novice troubleshooting this type of system. Any ideas of what could be wrong when only one radiator in the system does not heat up properly? If so, what steps should I take to eliminate or diagnose the problem?

 

How much pressure is on the system? In general, you need about 10-12# for a single story and an additional aprox 4# for each floor.
Where is this radiator in relation to the others & to the boiler? ie: first off the main, last off the main?
Any valves?

 

It took some time to get back since I was out of town for the week...
THe pressure gauge is reading only 11-12 lbs of pressure. This reading was at a time when the system was not calling for heat. (the pressure reading should be the same regardless if the system is calling for heat versus resting right?) I've been told that there is a screw or other mechanism to manipulate the pressure but I didn't see anything obvious on the fist pass. This is an apt size Weil Mclane boiler with an older circulator (not Taco style).

The boiler is in the basement and this is a 2nd floor apt, so I am assuming I will need 19-20 lbs of pressure, based on your suggestion, for water to get there and circulate properly. There is no valve above-floor for this radiator and it is a straight run up 2 floors almost directly above the boiler. The pipes run straight up thru a bedroom in the first floor apt. The tenant advises it takes 2 hours for this radiator to get lukewarm while the radiator in the bedroom gets oppressively hot even when the thermostat is set at 65 degrees. I am assuming this is a pressure problem since the current reading is much lower than you suggested and the radiator at least gets warm overtime (so I know water is getting, there albeit slowly). I will try to find the control and increase the pressure this weekend as you suggested.

 

You shouldn't need to go as high as 19-20#. 15-16# should be enough. The 10-12# for a single floor presumes the boiler to be in the basement. Here is one brand of pressure reducing valve. To increase the pressure, you would loosen the locknut & turn the screw clockwise.
http://taco-hvac.com/en/products/Boiler+Feed+Valves/products.html?current_category=115