Brewtus III-R.... WHICH Sensor Failed?

[Mike PDX]

Hi, my Brewtus III-R has has been a workhorse for the last 12 years.  There have been a few failures during that time period (PID, Pressure Stat, and Steam Pressure Gauge) but they really have been straight forward for me to fix.  However a new problem started a few days ago that has me scratching my head since I’m not sure of the order of operations the machine goes thorough when switching between Steam Boiler and Brew Boiler heating.  

Here’s what’s happening… Machine turns on as normal each morning, tops off water reservoir (it’s plumbed) and then commences the heating cycle - first stem boiler to pressure at 1.3 bar, then brew boiler for a bit, then back to steam boiler when pressure drops to .9 bar, then back to brew boiler, etc… until the brew boiler reaches 204F and PID float commences.

Everything seems normal right?  But after 60 to 90 minutes of being at temp, the steam boiler pressure falls and the heating element does not kick in at .9 bar, but dropping below that threshold DOES lock out brew boiler PID float, even though the steam boiler isn’t active.  Consequently both temps drop until there is no pressure in the steam boiler at all, and the brew temp hits ~150F (this temp seems to vary a bit from 130F at the low end to 165F on the high side) when the whole system comes back to life and the boilers start activating in sequence as they should.  Sometimes the brew boiler will make it back to 204F and PID float, but sometimes it only gets into the 190s before the temp death spiral starts again.  The only way to restore normal function is to shut down and allow the machine to cool for 20 to 30 minutes.

My initial thinking was that the “low” pressure side of the pressure stat failed, hence blocking the call for heat to the steam boiler.  But if that’s the case why does the brew boiler stay locked out if it's not sensing low pressure?  Also, why does the system function for 60 to 90 minutes before the temp death spiral?  My guess is that there is a sensor that fails when the internals of the machine hit a certain temp (e.g. why it only happens when the machine  has been on for a time) and I also suspect that it IS the pressure stat BUT, would love to get the wisdom of the crowd involved here before ordering parts, since the brew boiler lock out is making me doubt that.

Any ideas Brewtus people?

Thanks!

Mike

[Brian]

Hey Mike,

The reason the steam boiler is effecting the ability of the brew boiler to heat is because power to the brew boiler is routed through the pressurestat. The pressurestat has 3 prongs, one is the common where the power is fed in. One is normally closed which feeds power to the steam boiler, until the steam boiler comes up to pressure, and one is normally open which feeds power to the brew boiler solid state relay but only when the steam boiler is at pressure. This cleverly makes it so that the machine can have two good sized heating elements without blowing out your fuse/circuit breaker because both heating elements can never be on at the same time. If you have a switch that disables the steam boiler what it is actually doing is diverting power from the common prong to the normally open prong. It's possible that the little bimetallic strip in the pressurestat is not able to maintain contact with the normally closed switch as the body of the switch gets hot in side the machine. When this happens then it would be unable to heat the steam boiler, and since the steam boiler never reaches the set pressure the brew boiler never heats either.

Both boilers also have a safety thermostat that are supposed to kill power to the thermostat in the event of a pressure stat or temp controller failure. It's possible the thermostat on the steam boiler is acting up. These have been known to fail and are cheap and easy to replace.

The other posssibility, is that since all of the power for both boilers is coming through the relay box, that as the box gets hot it stops functioning correctly. These boxes have also been known to fail. If you feel comfortable working with a multimeter with the cover to the machine off, the best way to check what is happening would be to let the machine heat up until the problem occurs, and then unplug the machine and remove the cover. Plug the machine back in and start tracing to see where you are no longer getting voltage, test from the pressure stat common to neutral and check that you get voltage on both sides of the safety thermostat, that should help you narrow down where the issue is occuring.

Best of luck, be sure to write back with any updates!

[Mike PDX]

Thanks for such a detailed answer Brian!  I think my first step is to replace the pressurestat since it's due (replaced the first one ~5 years ago) and will see if that solves the problem before breaking out the multimeter ;)  Also, anyone have a source for the pressurestat pipe?  Or barring that can someone confirm the size, length, and thread type on both ends so I can fabricate one from parts?  I was able to reuse the old one last time with a CRAZY amount of effort to remove the plastic from the old copper threads, but was planing to order a new pipe this time after learning my lesson last time.  However, those pipes seem to be back ordered everywhere.  

Thanks!

m

[Dave B]

time to JUNK it.