Wacky Boiler Water Temp

Gary_8

My baseboard hot water heat boiler (gas fired Pennco of unknown manufacture date) has been exhibiting odd behavior.

The problem is that the temp of the water leaving the boiler (as measured with a temp probed strapped to the outlet pipe) is never as hot as the thermometer on the boiler or the aquastat indicate. The system has two zones (first floor and second floor) with two circuits (front of house and back of house) in each zone. A single common circulator is used.

The aquastat is set at 185. The boiler thermostat indicates between 180 and 190 (very small scale, difficult to read with accuracy). With one zone valve open, the maximum temp of the water leaving the boiler is 172. With both zone valves open, the maximum water temp leaving the boiler is only 150, even though the boiler is reaching the high cutoff and cycling off. There is no noticeable fluctuation on the boiler temp gauge with both zone valves open, is stays in the 180 to 190 range. I have tested the validity of the boiler temp gauge by leaving the circulator off but turning the boiler on (you can do this with the “Manual” button on the Honeywell L8148J aquastat) and opening the zone valves to let convection current trickle water through the boiler. When I did this, the max water temp exiting the boiler was 188.

So it appears that aquastat probe is in a hot spot on the boiler and that greater the flow of water through the boiler, the greater the difference in the temp between the hot spot and the water exiting the boiler. Is this normal? Can anything be done?

The heating system has a very difficult time keeping up in cold weather. The problem is that both zones stay open the entire time and only 150 degree water circulates through the system. Even on the coldest days, the boiler reaches the max cutoff and cycles off on a very regular cycle every few minutes.

Thanks in advance for any advice.

Unknown

Circulator

What is the brand of pump that is on this boiler and where is it mounted (supply or return)? In reference to the mounting, which way is the arrow on the pump body pointing? Almost sounds as though you are flowing the wrong direction and your supply water is actually your return water. Another way to test this is to check the temperature on the return pipe to see if it is hotter than the supply. Hope this helps.

Glenn Stanton

Burnham Hydronics

Gary_8

Glenn,

Thanks for the reply. Unfortunately, this is not the case. Have spent alot of personal time with my boiler. Boiler outlet pipe gets hot first, then comes back down the return manifold with the zone valves a couple of minutes later. Pump is on the return side.

Unknown

OK

But what brand and model of pump is on the boiler and what is the BTUH capacity of the boiler?

Glenn

Mike Murray

er, what is the temperature of the RETURNING water in relation to the outgoing?
if this "differential" fluctuates too wildly (should be around 20 degrees) then your building is losing more heat than it should. If it's fairly close (within 5 degrees) then check your rads for dirt and air blockage.