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Question DetailsAsked on 1/4/2018

Noritz boiler heats water for about 5-7 min and then shuts down-Why?

Noritz water circuit is hooked to a heat exchanger. Cold side of heat exchanger is hooked to coils in the concrete floor which pick up heat from heat exchanger to heat the structure. This is a typical in-floor heating circuit and this is the first problem I have had in 10 yrs.

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1 Answer


Ahhh - Noritz. Far from my favorite - seem to have a tendency to crankiness and leaks.

When you say cold side is hooked to coils in the floor, I hope you mean the fluid in the coils circulates through the coils - so both hot and cold are connected to heating coils.

First guess given recent very cold weather across much of the country would be frosting of the flue vent - but should not take 5-7 minutes for that, more like 30 seconds or less.

Does it have the electronic error code indicator on it - debugging of codes can be found in a table in the owners manual- also in first article below, most common ones in second article here -

My first suspicion would be freezing or restriction of the incoming water, causing it to run low on water - or liming up (they are real prone to that) so the boiler needs cleaning. For some people with hard water this is about a monthly thing - so if you have been running 10 years without doing that liming up would certainly be my first thing to look at. Causes boiling in the tank.

Restriction of water you should be able to check by operating the drain valve (beware - HOT water) - if it flows continuously for more than a few seconds and at good pressure (like from a faucet) incoming water should be fine.

Course, is that 5-7 minutes unusual ? Many boilers only operate for a minute or two to get a hydronic heating system back up to heat unless the outside temp is real low - so if it usually goes more than 5-7 minutes must be a really undersized system or it is unusually cold outside. Do you know that it is shutting down itself, not just being cut off by the thermostat in the house reaching the demand temperature ?

Also, if it is short cycling (compared to usual operation) check the return pipe temp a bit away from the heat exchanger - if the return pipe warm or hot, or cold - if cold, is there a chance you have a frozen place in the piping so the water is not circulating, causing the boiler to heat the boiler and maybe the exchanger but not the loops, making for a short cycle.

Also, a failed zone valve can do this if your unit is programmed to heat only on demand - the thermostat may be putting in a demand for heat, so the boiler fires - but if a zone valve is not opening there is very little water to heat, so could be short-cycling for that. Check temp in pipes (WARNING - HOT) on both sides of zone valve (about a foot or more away on outbound side) - if outbound pipe is not hot when thermostat is demanding heat, then could be a failed zone valve or broken wire leading to it.

Failed circulating pump, and failed thermostat (dead batteries maybe ?) can also cause this. Also, many boilers are programmed to reheat once they reach a certain low temp so there is hot water available at all times - could it just be reheating the boiler (maybe because it is in a cold or unheated area) but there is no demand from the thermostat so it is short-cycling ? For instance, my boiler, which cannot be programmed to less than 140 degrees, typically (unless about azero or below outside) probably refires 2-3 times to reheat the water in it for every time it fires to reheat circulating water running through the loops.

One other possibility - if the air relief valve has failed, it would not be releasing air from the unit, causing it to fill with air and cause premature boiler overheat shutdown. Failed inlet valve can also do this - not allowing makeup cold water in to replace the small amount lost as steam through the air relief valve(s).

If above does not help, then Heating and A/C (also some Plumbing contractors) would be your Search the List category to find well-rated and reviewed firms to send out a tech to work on it.

Answered 2 years ago by LCD

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