Weil McClain Short Cycling

Jim_90

Hi, Just replaced my Bethlehem Dynatherm with WM WGO3 with Amtrol unit. It appears to operate somewhat differently (i.e. now low limit) and I am curious if it is operating correctly. 1) The burner comes on as soon as hot water is called for even if the Amtrol is up to 115. Is this appropriate? 2) Is the burner set to come on as soon as one of my 4 zones calls for heat regardless of the boiler water temperature? 3)I have noticed at random times the burner comes on for 50 seconds and then shuts off even though the high limit has not been reached. This happened 5 times in a two hour period last night. The temperature was 145 degrees when it came on. Is this appropriate? What would cause that to happen - come on and only run for less than a minute?

Many thanks, Jim

Weezbo

it would depend on the flow rate and what is happening ...

with the various zones....the temp well notices these temp changes maybe a little more rapidly than the indicator on the boiler....

Brad White_153

What Weezbo suggests

is a good start, checking the coincidence of zone demand to your boiler firing, which will answer your second question.


"Normally" is a subjective term but the most efficient way, if the boiler is firing based on temperature, is to open a zone valve or circulator and let the boiler respond when it needs to. As Weezbo said, the internal well, if used, has better accuracy, more direct and into the fluid.

If your boiler has a fixed operating temperature I would check the actual limit settings and the controller and if there is an adjustable differential, the "bandwidth" total above and below your actual setpoint. It may be too narrow. Just guessing here, I do not know what you have for controls.

Setpoint: Might you have outdoor reset and not know it? Is this possible? A cast iron boiler often has a low limit supply temperature of 145 or 150F. This is not uncommon because the goal is to keep the return water above 130F.

You may also have short-coupled zones, with low volume and high flow rates. When the zone calls, the water races through and comes back not a whole lot cooler than the supply temperature. This can cause short cycling.

Some thoughts, hardly all possibilities for sure.

mark schofield

I put in a WTGO3 last winter and found the recovery time/cycle with no load to be 3-4 minutes. With the Honeywell aquastat set to 180-160 with a 15 degree differential. Even with a zone calling the boiler goes to high limit very quickly. If your boiler came packaged with the Honeywell controller, here's a link to it which tells how it should work. If that's the problem. Possibly a place to start.

http://customer.honeywell.com/techlit/PDF/95-0000s/95-6571.pdf#search='honeywell L8124 c'