TT Prestige Error Code - LWCO open?

Margaret Ross

Hi-



Just trying to do some troubleshooting before we call in the cavalry...first chilly day of the year and our TT Prestige 110 woke up with an error message. The display is flashing between 9 66 and (I think) b 26, which the manual says is due to "Factory supply LWCO device or external limit (terminals 15 & 16) is OPEN. Burner off for 150 seconds auto repeat." It does cycle through as displayed, but it stops after about 10 seconds and starts flashing again.



I looked in the installation and the owners manual for anything indicating a terminal 15 or 16, but saw nothing.  So, where would I find the low water cut off, and is it supposed to be open? (I don't know whether I even have one - don't know whether they're required in my area). If it isn't, should a non-professional be attempting to close it? And if it's not the LWCO, what is an external limit...and how do I close that (if it's supposed to be closed).



Thanks!

Gordan

Is your system pressure under 7 psi?

Sometimes there are slow leaks in a system, and over time the system pressure will drop. What does the gauge on your TT indicate?

Margaret Ross

Just under 10 PSI...

Doesn't look to be 7 or under, but it's close.



Can I fix that by just re-bleeding the radiators?



Thanks!

Gordan

No

You need to add water to the system. Can you post a picture of your boiler and its surroundings? There should be a valve that (dis)connects it to/from the domestic cold water supply. You may (should) also have a pressure reducing valve and a backflow preventer.



There's also the issue of the leak. Can you see any evidence of where the piping may have leaked? How long has this been in operation since the last system fill?

Margaret Ross

New system!

Thanks! The system was installed in Jan. 2009. There are no signs of leaks (that we can find). Last year we redid our basement and created two zones - one for the main house and one for the new basement. We had to drain and re-fill the system then. That would have been December of 2010.



We have had pressure problems before - in 2007, with our old boiler, there wasn't enough pressure to bleed/fill the upstairs radiators. We also had to have the system drained and refilled once before in 2007 or 2008 when one of the radiators would not heat, and no amount of bleeding would get it to fill with hot water.



We've been in the house for 4 years, and we have yet to go through a year without something in the system not working. I thought our troubles would be over after replacing our 35 year old monster with our beautiful (and friggin expensive) TT.



I'll post a photo when I get home tonight. If I could learn to resolve these problems myself, we'd save a lot of money every year. Thanks!

Gordan

All these problems seem to have a shared cause

Namely, low static fill pressure. It has to be high enough to maintain a column of water that's as high as the vertical distance between your fill point, and your highest radiator. It also has to be low enough that, once the water in your system has heated up, your pressure relief valve will not pop. You're right that no amount of bleeding will get the water into a radiator unless there's enough pressure to overcome gravity. Nothing likes to go uphill without a little push.



What kind of radiators do you have? Maybe your expansion tank is too small for your water volume, and thermal expansion WAS causing the PRV to pop until enough water was shed from the system to put you in your current fix.

Margaret Ross

Gordan is my new hero

I located the water backflow preventer and the water inlet and let in enough water to raise the pressure to the factory startup setting of 12 psi and the water started heating. YAY!!



If it drops again before Monday (which is when my installer/maintenance company comes out for their annual checkup) I'll know better what to say. Either there is an unlocated leak in the system that causes pressure to slowly drop over the summer when not in use, or, when it started up it built up too much pressure and popped the PRV.



It's possible that the expansion tank is too small - I haven't done the calculations for water volume. re: what kind of radiators we have...hot water radiators of all shapes and sizes, I don't rightly know what your question means. Size? type? In the basement we have cute little euro radiators that look like they could be towel warmers, and in another room we have a giant thing that's almost almost a full foot wide. I love learning this stuff, so if you'll tell me what to calculate, I'll calculate.



I LOVE HEATING HELP!!!!!!!!!!!!!

Gordan

Aw, shucks...

Just trying to give something back.



Before you declare victory, though, let's dot the tees and cross the eyes. It is possible that there are now air pockets at the top of your system, since the low pressure inside the piping could actually dip below atmospheric at the top (the weight of the water is pulling it down, and there's not enough pressure to keep it up), create a relative vacuum, and suck some air in. So, now's a good time to bleed those radiators. Do you have a pressure reducing valve? It should be between the backflow preventer and the boiler, and its purpose is to add water to the system to maintain it at a preset static pressure. If you have that, then leave the "isolation valve" (that's the [typically] ball valve between the backflow preventer and the domestic cold water) open while you bleed your radiators. That will ensure that there's no large pressure drop as a result of bleeding. You can close the isolation valve after you're done bleeding the radiators.



If you don't have a pressure reducing valve, then bleed, top off if necessary, bleed some more.





Watch the pressure during a heating cycle. How high does it get, and what's the boiler water temperature? (The boiler displays that.)

tim smith

TT prestige fill pressure & lwco probs

We too have had to make sure our guys set the fill to 15psi min to keep from having low press lockouts. This way there is a little buffer between min press and set pressure. Also, clean low water cutoff probes every year or two while doing maintenance as they will get a little coated from water impurities and shut off on false lwco signal. Good luck all, Tim

tim smith

TT prestige fill pressure & lwco probs

We too have had to make sure our guys set the fill to 15psi min to keep from having low press lockouts. This way there is a little buffer between min press and set pressure. Also, clean low water cutoff probes every year or two while doing maintenance as they will get a little coated from water impurities and shut off on false lwco signal. Good luck all, Tim