Best Hot Water Boilers in Seattle WA

They came quickly, were super friendly and fixed it the next day. Great people. Not cheap but quality is worth it. Use these guys.

Watch out for these guys, as they will try to rip you off as much as possible! Very dishonest people.
They inspected our 5-yr old tankless water heater and identified that a part had to be replaced. After we gave them the go ahead on replacing the part (heat exchanger) worth < $300, without our consent, they replaced the whole unit (which they provided themselves with a 60% mark-up for $2,000). And then they threatened consequences if we didn't pay the price immediately.
When we asked in a respectful manner why the mark-up was unreasonable and why we hadn't been notified of switch from part replacement to unit, Evan (owner) started using curse words and started threatening.
After we paid them, we asked for our old unit (one day after their service), they said they had tossed it out and it couldn't be retrieved.

Having said all of that, they responded promptly with a same day service and everything was back online and working after 3 hours, so if you don't mind them stealing from you, this business can be a good choice.
We recommend getting a 2nd opinion if they tell you the unit has to go.