Boiler System No Heat

rav1964

have boiler system in an apartment complex, it feeds 8 units. in one unit there is no heat. the plumber has drained the system and replaced the t-stat. when the system gets drained and filled back up there is heat for a while and then no heat. the system was repiped due to a fire, is it possible that the hot supply line that goes to the unit got plumbed back to the hot supply line and not the return. thanks

gene2

Sounds like the air needs to be bled out of each radiator. Sometimes it takes multiple bleedings. This has to be done each time a line is drained. A competent heating contractor will know this.

rav1964

they have bled out the system and the unit several times. thanks

beenthere

Is this apartment, the highest one above the boiler?

Could still be an air problem. If they had to change some piping to this apartment. they may have accidentally piped in an air trap without realizing it.

What pressure is the system running at.


PS: Draining a boiler and filling it up with fresh water, is one of the worse things you can do to a boiler system.

rav1964

its a lower unit. each unit is piped off the main line hot supply and then returns to the main return. one thought is that the line is going from the main hot and returning to the main hot instead of the return causing the water to stay at the same temp at in the lines. i think the pressure is 40 or 50 psi. the piping is in the cieling and then runs down to the unit

beenthere

It the supply and return of this unit were both piped to the supply manifold. You wouldn't get any heat. Anytime. You would get hot water out of the bleeders while bleeding. but thats it.

40 or 50 PSIG? Is the boiler rated for that pressure. Many aren't.

Piping in ceiling and then running down to unit. Is an indication of air troubles. Does this line have a purge set up on it? It should.
Next. What circulator is being used. It may not have the ability to over come the head pressure, of trying to force hot water down, and cold water up. Incorrect sizing of a circulator is a common problem.

rav1964

we dont have heat. i think we will open the cieling and check out to make sure the lines are not crossed. also pex was used, would be an issue?the boiler/pump are existing only thing done was the repiping to the units. thanks for the info i will be out there monday and check this out. will post what i find and thanks again for the help!

beenthere

Using pex instead of copper. Can increase the head the circ must work against. So if 3/4" copper was replaced with 1/2" pex, it more then doubled the resistance to flow.

rav1964

thanks for the info beenthere, i will be over there next week. the pump on the system pumps out of the boiler to the units. i need to add the system is in the center of the building and feeds 32 units. only have a problem with the replumbed side

rav1964

we checked the lines today. all is hooked up correctly. the return of the apartment in question is at the end of the return. the main supply and return are one loop and the return is at the end of the loop. would this cause no heat in the unit. also all the pex was sized properly.
thanks

beenthere

Dumb question. How did you determine the pex was sized properly.

You need to know the PD it has for its length , at the GPM you need to flow through it.

Most likely. The pex is NOT sized right. And is increasing the systems head pressure loss above what the circ can move the amount of water you need.

You probably need to increase the size of your circ. Might want to use a Taco 0010 3 speed. And adjust its speed to the one that provides good water flow, without noise.

I'm just guessing that a 0010 will work.
Can you post the brand and model number of the circ.

rav1964

the pex was sized by the manufacturer

beenthere

Ok.
You told them the flow rate required, and the BTu output needed for each rad/baseboard, and the average temp those emitters need. And thats how they determined what size to use, and what head pressure increase it would be on your circ. And then told you that your circ is able to handle the additional head pressure.

Right?

Meaning you have different sizes of pex running to your different baseboards/rads. Because ¾" pex, doesn't flow as much water as ¾" type M copper pipe.

Or did they tell you to use a different sized circ?

beenthere

Its always possible, you still have air trapped in the pex.

Does it sag anywhere.

BCConstruction

Was the system balanced?

72chevy4x4

does the apartment have a radiator or an HVAC closet w/ heater core and air handler? If you have heated water one one side of the radiator how can you not have heat...is something impeding flow?

BCConstruction

There's a few reasons for this. Air is the main reason, Sludge build up in the rads but normally take over 10-15 years before it's so bad that the rad stops heat in all areas and the next is system balanceing.

If it's air then only a certain % of the bottom of the rad is going to get hot. But if the rad is getting hot from the top to bottom but not all the way across then Balance the system, If that dont solve it then it could be sludge. What colour is the water when you vent the system? Your pump could also be faulty like broken impeller or clogged. What kind of system is it? Open vent or closed loop/sealed system?

DuMass

This may sound like a dumb question, but… is the circulator pump for that zone installed correctly? I’ve seen them installed backwards before.
I’ve also seen small 3-phase 3-HP taco circ pumps running backwards because the motor wiring was reversed during replacement and nobody bothered to check for proper rotation at start-up.

rav1964

thanks for all the replies, the loop was terminated and now the apartmant in questions has heat and its been working for the past week.
thanks
again
rav