When you have an intermittent problem in a system, such as your heating system or your car or your body, you have three choices:
1. Invest time and money for a diagnostic system to catch the event when it occurs and record the status of the system; like a flight recorder for your boiler system.
2. Keep trying to fix it by replacing things that may not be broken.
3. Accept the idea that it may be benign and watch and wait for more evidence that it may be a symptom of a serious problem.
Since we aren't talking about a risk of inoperable cancer or a massive heart attack, I suggest the third option. That is what I am doing with exactly the same symptoms that you report.