Boiler pressure gets very high. Water temp is low...

Sweet_Lew

Hey All,

Ever since I installed a new digital thermostat (replaced a mercury bulb Honeywell) the boiler has been running erradically. Example..I set the thermostat to run 74 in the morning. Then I have it set to 71 for when we leave for the day and back to 74 when we return starting at 4:30 PM (It was 15 degrees as a high today btw). I got home at 5:30 and noticed that the thermostat was only reading 73. I checked the boiler and the pressure was at 25psi and the water temp was around 150. The radiators were really hot and so was the circulator pump and all the pipes in the basement. I turned the thermostat down a couple degrees to bring the pressure down. It finally stablized and the pressure is holding at 20psi hot and the water temp is back up to 160.



This ALL started happening with the new t-stat. Could the t-stat be faulty in reading the room temp or could it be due to the extreme cold? Could the aquastat have gone bad?



 Again, I did not have these issues with the old Honeywell. From now on "if it aint broke...don't fix it...

John Mills_5

It may be

That the boiler is having trouble recovering from 71 to 74 in that bitter cold in the time frame you are giving it. 74 is fairly toasty for a very cold day. What's your aquastat limiting out at? Is this baseboard or large radiators? The pressure issue sounds unrelated. 

Sweet_Lew

Probably right

Thanks for the reply. I was thinking that too regarding the the boiler struggling, but we never had this issue with the old t-stat and it was brutally cold in December. We have radiators..All different shapes and sizes throughout the house and they are running really hot too, but the house just doesn't seem as warm with this new t-stat. I think it has something to do with the old one having an anticipator.

The aquastat is limited to 180 degrees.

CMadatMe

Scratch, Scratch

May I ask what a thermostat has to do with boiler pressure? Why are you running at 20lbs? Do you live in a 4 story house?

Sweet_Lew

Not sure

I'm a noob at this hot water boiler stuff, so I'm just throwing out possible ideas. All I know is these problems started when the new thermostat was installed. The boiler reads 15psi when cold, but 20psi when running\hot. We have a two story house with the boiler in the basement. Now, not sure if this helps or not, the basement is not insulated so it is cold down there..

I'm thinking I may need to call out a pro..Any other ideas?

John Mills_5

Unless

it is a very low end new thermostat, should have some kind of anticipator or cycles per hour adjustment. Look in the manual for CPH. You'd want around 2 for a hot water heating system with big radiators for longer run periods.



If the sucker hasn't been checked by a pro lately, might not be a bad idea. See why you are getting 25 psi. That's getting up there. Might need a tank drained or replaced.

Sweet_Lew

Yay....

Well, the boiler was serviced in the fall by a Bryant factory authorized service tech. He stated that cold pressure was perfect (15psi), the expansion tank was empty. The t-stat does have a CPH setting and it is set correctly at 3. However, being as cold as it was the past couple of daysm the CPH settings gets thown out the window and the t-stat kept running the boiler constantly to keep the set temp. However, I am changing it out with a RobertShaw model that has an anticipator setting like the old mechanical I had.

So I decided to call the repair place who serviced the boiler in the fall. They wanted $125 for a service call on the weekends. I then called a local guy who has come out before to give me estimates on Space Pak and Unico systems. Instead of booking a time for tomorrow, he called me back and asked a few more question. He explained to me that the thermostat was set too far back for current outside conditions (15 degrees or colder) and the boiler was struggling to catch up to the set temp when the program cycle changed. That would cause the rise in pressure and making the rads get super hot. Pretty much everything I described to him was normal due to weather conditons and me setting the tstat back too far. From now on, if the weater is this cold, I should just keep the temp static.  He said if the pressure builds past 25psi again or if the pressure relief valve starts to leak to call them back. I just saved $125...

Lance

Seems to me

Seems to me you have two problems, one the control and two the pressure. The pressure is now looked at because you have a problem. The pressure fix is to make sure the expansion tank is properly charged and you start with 12 PSI for a two story home.  You should be able to reach 200-240F without going above 20PSI with a properly sized expansion system. Your hi limit can be set as low as possible as long as it is enough for the sized radiation. 150F would be the lowest I'd go. Most systems set at 190F and are designed for this. Ignore the pipes are hot when you get home you never know when if it

Two, the thermostat wiring is critical to match what you have.

Sizing and capacity are concerned with set back temps, not just controls. The greater the setback, the lower the outdoor temp,(the higher the heat demand), and the quicker you want a response means the larger the system has to be. And often too large means no savings. Some setback can save money, but a perfect sized system is designed to maintain a single point temperature and unless the demand is low, return to setpoint may take longer. Good luck.

Sweet_Lew

Thanks Lance!

Thanks for the reply. So here is the current status:

I turned off the programing and the t-stat is set for 74 degrees (but stops at 75 as it is programmed to do so). I'm still creeping towards 20psi when the boiler is running but the water temp is only hitting 120-130 degrees. The aquastat is limited to 185 degrees. The rads are warming up but again the house feels cooler than with the mechanical. Again, this all started when I changed out the t-stat. I will be installing the old one or a newer mechanical with an anticipator this weekend. Wondering if I should get a pro out to check the system.