boiler high temp cut off

bauer

Hello --

Boiler question -- hot water rads. While my t-stat is calling for heat, my boiler will run and keep hitting the high limit set point (180), and the burner will cut off. The circulator obviously continues cycling water.

Is the goal for the burner to be firing at all times while there is a call for heat? If so, is my problem caused by an oversized boiler and/or improper/too fast flow?

Thanks!

bauer

Gotcha..thank you this makes sense. Let me add a few details:

the house was originally piped as one zone and required a bypass loop with ball valve to allow some hot water into the return because it was coming back too low. The comfort in our house was less than ideal.

I have split off into 3 separate zones now, and obviously this cycling is happening when only 1 or 2 of the zones are on (thus less heating demand). Am I correct in trying the two following options to help correct the issue:

1. One of the heating zones is piped with a manifold that allows for flow control to each rad. Slowing down the flow via the manifold should bring back lower return temps and help, no?

2. Given the new variable heating demands, I was also planning on swapping the circulator out for the Taco variable speed model to help regulate return temps - is this still a good idea?

Thanks again!

bauer

I see... so you mentioned most boilers are oversized and do cycle the burner... how much is too much cycling that I would consider a buffer tank? In other words, how long should the burner run in comparison to the circulator for it to not be a concern?

Second question, if my supply temp is 180, and 160 would be an idea return temp, what temp is too low? I amy currently seeing returns of between 155-170 depending on how my flow is adjusted on the manifold.

bauer

Great info, thanks for answering.

Before I separated zones and started using a manifold, startup took forever. The boiler would easily run for an hour or two just to get return water up to temperature; thus the bypass loop to prevent cold return water.

Since moving to a manifold, I am seeing much quicker response from the radiators; I haven't timed them yet but they get warm much quicker. I will time the return temp climb next time the boiler is somewhat cool.

The boiler is a weil-mclain; originally oil-fired but converted to propane with a Carlin conversion burner

bauer

great advice, thanks.

to be clear, my system *had* a very high mass. I eliminated all of the large cast iron pipes for various reasons, thus eliminating my 'buffer' tank.

I will keep a closer eye on the burner over the next several days to see if it is running for 10min or less and make a call at that point I suppose...

with respect to heat loss, it is on my list of things to do as I am curious how well this boiler is sized also. I suppose that will also help my decision.

Paul48

Propane Hat

Paul48

How did you plumb the 2 zones that are not off the manifold? Two pipe? What size pipe?

bauer

short answer to that is, i am only running one zone right now; so i am not surprised that the boiler is short cycling (it is only feeding 6 radiators when it usually feeds 13). I was just trying to get an idea of how short is "too short" and how long is 'acceptable'.

long answer is, here is my new 3 zone setup (yet to be utilized):

- 10-radiator manifold split into two zones using mr. pex actuators. 1/2" pex to each rad.

- 3rd zone is a 5-radiator two pipe set-up in a section of the house where the existing piping is not readily accessible. it is piped using a 1" taco zone valve, tied into all the existing piping. I have a gate valve to manually adjust flow if I need to, and thermo's on both the supply & return.

Paul48

I'm sorry, I was led to believe that you had replaced the original piping(from your other posting). If that was the case, how it is piped and pumped can affect short-cycling. You seem to have gotten the answers you're comfortable with. Best Wishes