2 radiator no heat -- hot water boiler system

I have a hot water boiler system, with 4 zones (ie. 4 thermostats). And it is a 2-pipe system (one hot water in, one hot water out). In one of the zone, there are 10 radiators connected to it (7 radiators at 1st floor, 3 radiators at 2nd floor). Out of these 10 radiators, 2 do not have heat (and they are both at 2nd floor). I tried bleeding them, there are some air coming out initially, after that there are only a stream of cold water coming out. The other radiator at 2nd floor in the same zone works perfectly (ie. when switched on, it's very hot).

I see circulators above the boiler, so I assume this is not a water pressure issue.

See attached pictures of the boiler, the psi reading, the radiator that doesn't have heat, and the radiator valve.

Any suggestions on what I should try next?

 

A,
Increase your boiler pressure to 20 PSI and see if that makes a difference. If your gauge is correct your pressure looks low. After pressure has been raised check system again and bleed those convectors if necessary but I don't think you have to.

Those caps on the vents should be loose for automatic bleeding of air unless they are leaking in which case you can tighten them until replacement or just loosen to vent.

Hope this helps a little.

 

Hi, thanks for the suggestion. I pulled the lever of the attached device to increase the water pressure. I can definitely hear water flowing sound when I pulled the top of the lever. So far I haven't seen the water pressure increase. Shall I pull the lever for a longer period of time?

btw: I just used my tire pressure gauge to test the water pressure of the expansion tank, and it reads 13 psi.

 

If you check the tank pressure while in the system without removing it or depressurizing the system it will read whatever your system pressure is. The tank must be isolated to get proper reading.

As far as the lever goes, yes, raise it until you see 20 PSI on the guage.

 

The pressure expansion tank pressure you measure with a tire gauge will, in almost all cases, be the same as the system pressure. To try Spott's suggestion, keep temporarily raising the pressure to 20 psi as shown on the boiler gauge.

What you identify as a radiator valve is actually an air eliminator device. You can remove the cap from the Schraeder valve, and press downs the stem to see if air comes out, thus bleeding the radiator.

 

Having the zone thermostat on a level different than some of the radiators in the zone is a poor design. The zone radiators on the level without the zone thermostat do little to satisfy the thermostat. If the feed and return lines for the 3 zone radiators on the second level are accessible in the basement, I would consider moving them to their own zone with a thermostat and circulator or adding them to a existing zone on the second floor.

 

I've been trying to increase the water pressure in the boiler by pulling the lever on the water pressure regulator, but seems the psi reading barely moved. I noticed the label on water pressure regulator says 12-15 psi, seems can't increase pressure to 20 psi? I checked the pressure on the expansion tank again, and it's still 13 psi.

Also, I noticed there is some water dripping out the relieve valve, I don't think I ever saw water dripping out from relieve valve before. Maybe related to me trying to increase the water pressure? The label on the relieve valve says 30psi.

 

Your pressure relief valve is set to go off at 30 psi. If it is starting to leak I would guess it's because of increased pressure and I wouldn't add any more. You may have a faulty pressure guage and the needle might be stuck.

Did you try running your boiler to see if you have heat to those 2 convectors.

When you added water could you hear it going in. Did the feed pipe get cold, did you hear any air coming from your vent where you're feeding.

I would let a little water out until relief valve stops leaking and replace the gauge so you can see what is going on.

 

Look on the boiler's name plate for the words Maximum Allowable Working Pressure or MAWP. There should be a number stamped there, most common is 30 but it could be as high as 60. Since the pressure gauge has a red line at 50 psi I suspect that the MAWP is also 50.

The safety valve should have the same set point as the MAWP. If it doesn't you can install a higher rated safety valve provided that no other component of the system has a lower pressure rating.

I suspect that your pressure gauge is reading incorrectly and needs to be replaced.

 

Yes, MAWP is 50 psi. I agree that looks like the pressure gauge is not working. Although the temperature gauge is working, I can see clearly temperature change.

I'll probably wait for a couple months to replace the pressure gauge, I'm not quite comfortable draining the boiler and refill in middle of winter.

 

Just to give an update on this. As I said in the last reply 3 weeks ago -- I'm not comfortable draining the boiler to replace the pressure gauge in middle of the winter, so I did nothing.

Then this morning, I noticed that one of the two radiators that do not work on the 2nd fl is heating!! Although the other one on the 2nd fl still doesn't work.
Because the one that now works is in a bathroom that I rarely use, so I don't know when it magically started working. Any one has explanations?

I still plan to replace the pressure gauge when spring comes.

 

Is there a single loop around the basement? If so is there a supply pipe to a radiator coming off the loop and a return pipe coming back to the same loop pipe.If so this is a monoflo system. If it is a monoflo system all supply and return pipe must go uphill all the way. I have seen many times one of the pipes to or fro the radiation had a bit of a belly and if drained that radiator would stop heating. Getting pressure up a bit, pump away from the expansion tank and the little it of air causing the problem would move and start working.

 

I have a 2-pipe system (one hot water in, one hot water out), i.e. not a diverter-tee monoflo.