How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask MasterFixIt Your Own Question
MasterFixIt, Handyman
Category: HVAC
Satisfied Customers: 9568
Experience:  Handyman
Type Your HVAC Question Here...
MasterFixIt is online now

Ultracom 30cxi hot water dropping to low flame after a min

This answer was rated:

Ultracom 30cxi hot water dropping to low flame after a min or two

New plate exchanger fitted today. Hydro block filter is clean. Thermistor values appear correct ( temp measure by pipe clamp so temp of pipe rather than water)

Flow sensor operating pink wire 4.8volts doc white wire 2.4volts grey wire 0.0 volts

When at rest flow sensor is the same apart from White is 0.0volts
The temp difference between flow and return is 30 degrees

Any ideas?
I am Tech Michael and I will be assisting you today.
Please be patient with us as these are technical questions and some testing may be required.
It may take a bit of back and forth conversation to be sure we have all the information in order to make a proper diagnosis.
Please explain clearly, is this unit leaking from the pressure relief valve or somewhere else?
Thank you
Tech Mike
Customer: replied 4 years ago.

Hello Michael,


The boiler is not leaking or losing pressure in any way.


I have since discovered that the boiler will do its job if i drop the temp of the hot water to 45 degrees. if i raise it to 48 degrees it drops to a low flame. it is a little perplexing.


for your information it is my own boiler at home. I am a gas safe registered

fitter qulified to work on boilers

Awesome Andrew, let me see what I can find, that sounds like a control issue for sure, but we will get to the bottom of this.
Please rate kindly, it will lock us in and you and I can reply back and forth until we solve this;-)
Its Sunday so it may take until tomorrow, I don't want your question to time out or end until were done.
Thank you Andrew.
Tech Mike
MasterFixIt and other HVAC Specialists are ready to help you
Customer: replied 4 years ago.

Thank you,


I have checked all of the normal problems. the boiler works ok at 45 degrees. which is ok.


however 45 degrees is a perfect temp for breeding legionnaires disease, so i would like my boiler to push out max temp from time to time just to clean the pipes.





Thanks Andrew, I agree, but that is somehow causing the issue when you run it hotter.
Please try setting the temp a bit lower than max and let me know how that goes.
Thank you
Tech Mike
Customer: replied 4 years ago.

evening mike, sorry for the delay with my reply. i have been out doing the day job.


Boiler runs ok at 45 degrees. at 55 degrees it still goes down to low flame. It also goes to low flame at 48 degrees.


max for boiler is 62 degrees.


thanks Andy

Hi Andy,
In this case I would have that checked. This is usually a fault with one or two things here. Either the main control unit has a problem or the Aqua stat is failing. But I suspect the main control has the problem.
You could replace that part if you are a little handy, don't worry I will help with that if you want to do this.
Please let me know Andy I can also help you find a replacement part as well;-)
Tech Michael