View Full Version : Boiler not operating within Hi Lo limits

12-07-2010, 08:16 PM
I have a Teledyne Laars Max D100 Boiler w/ indirect hot water. It is a cold start boller. It has separate Hi Lo limit controls. Hi limit set at 200F, Lo limit set at 180F. Problem: When thermostat calls or heat, boiler heats up to about 165F & burner cuts out. As water circulates boiler temp starts to drop. When boiler temp drops to about 155F, burner kicks back in & heats up to about 165F again & continues back & forth until thermostat is statisfied. Why isn't boiler operating between the Hi Lo control settings?

12-07-2010, 09:28 PM
Does it have an outdoor reset controller? If so, it adjusts to the load and outside temperature and overrides the manual settings.

12-08-2010, 05:22 AM
No Outdoor controller.

12-08-2010, 01:14 PM
This boiler probably has a safety high-limit aquastat in addition to the operational high/low settings. If the safety is set (or has failed) to 165F (lower than the operational high limit) it would exhibit this sort of behavior- kick off at 165F, back on again at 155F, repeat...

Is this (http://www.laars.com/LinkClick.aspx?fileticket=YaCxLGINeMc%3D&tabid=1609&mid=4036) the boiler in question?

If it's this series or similar and you incorrectly assumed the safety aquastat to be the low-limit, that could be the whole issue. (although 165F is way lower than the 180F you set it to.)

What model aquastat(s) does this beast have?