Despite what has been circulating around the 'net (originating from YouTube, but I do not want to point fingers at anyone), I want to make it clear that there is no proof that Alessa's powers interacted with the basement boiler which caused the explosion. It's an alternative fan theory, and is not by any means, factual.
Let's look at the Fire Article, which says,
"Investigations show source as basement of Gillespie home. Blaze now believed caused by malfunction of antiquated boiler."
The article does not state the boiler was the cause, only that it's believed to be the cause. The purpose of this article is probably there to show what the public believed. The Silent Hill Guidebook goes further into this, stating that a fake corpse was left behind at the scene, which was prepared by Kaufmann. It's likely a cover-up by the Order. Just because something's published in a newspaper, it doesn't meant it's true, after all, you don't believe everything you read on Fox News now, do you?
Now let's look at the Manifestations of Delusions article.
""Poltergeists are among these. Negative emotions like fear, worry or stress manifest into external energy with physical effects. Nightmares have, in some cases, been shown to trigger them."
Now let's take a look at all the notable evidence supporting that Dahlia intentionally used fire to immolate Alessa in a ritual, or something similar to that effect.
- Book of Lost Memories -   "She conducts a ritual to bring about the coming of the cult's God, inflicting extensive life-threatening burns upon her." and "the cause of the fire was a ritual that Dahlia conducted using her daughter Alessa in order to bring about the coming of the god."
- Harry's Notebook - "that was the young woman burned by her mother as a sacrifice to God... Alessa Gillespie."
- Sacrificial Book - "In another sacrificial rite mentioned in the same book, the victim is burned alive. This was a more dignified ceremony in which prisoners and sinners were not allowed to participate. Only the clergy could be sacrificed. Similar to burning at the stake, no comparable rite can be found in religions practiced nearby. It may have some connection with the main deity being a sun god."
- Silent Hill Official Guidebook  - "Q: What was the cause of the fire that broke out seven years ago? A: A ritual that Dahlia performed using Alessa."
- Altered Police Report implies that the Fire Article memo was altered to include that statement about the boiler.
So... the bottom line is: don't believe everything on the internet, no matter how many times it's circulated around, or by how many people believe in it. You do not swallow 8 spiders in your sleep each year, nor does chewing gum stay in your body for decades if you swallow it. Think for yourself, don't always let others think for you.
More-or-less, don't make such a big deal out of it. Silent Hill 1 is a 14-year-old video game meant to entertain. It's not particularly relevant to most people's lives nowadays anyway.
/end of rant