Curse you #IceStorm2013, my hydronic heating system froze!
Are you like so many other Torontonians, having suffered an extended power outage this past week? Do you have frozen heating pipes and or radiators?If so, you can damage your boiler if you try to restart the boiler while the system is frozen. This can cause thermal shock that may crack the heat-exchanger leading to a costly repair.
You need to know a safe manner in which to restart your boiler without damaging it and to avoid a lengthy and expensive repairs. If you book a service call to have a heating technician restart your system it will cost a fair bit as well, typically more than a couple hundred bucks.
The following, in simple layman's terms, are the steps to restart your system safely.
DISCLAIMER:
Among my qualifications I am a gas fitter & HVAC designer so i know what i'm speaking about, but if you read beyond this point or use the following information you accept all liability for your actions, and you understand that you are using this information at your own risk. It is provided for entertainment purposes only.
First a little terminology to help determine if this situation is applicable to your home. Hot water heating systems, are called hydronic systems. They traditionally use a boiler connected to radiators by hot water piping. They use circulated hot water to heat your home.
NOTE: I am not discussing a steam boiler system which uses pressurized steam to heat your home. Steam systems are far less common in residential homes in Toronto, you should know if you had one.
Hot water is circulated by an electric pump to distribute heated water to radiators in eah area of your home.
In a power failure the pump shuts off, as does the boiler's burner. As your house cools, the water in the piping and boiler can freeze at any point of the system. The piping, radiators, pump and boiler are all vulnerable, but typically, the system it will freeze in piping close to cold exterior walls first such as at exterior radiator locations.
If you restart the system with frozen piping sections it will impede the flow of water within the system. Heat will fail to leave the boiler, causing it to built to an unsafe level, at which point a safety control will cause the burner to shut down. Once the temperature falls to a safe level again the burner will restart.
Unfortunately, before the system has time to shut down the boiler's burners, the quick change in temperature from freezing to extreme heat and the resultant fast expansion of the metal can cause the heat-exchanger to crack or split, particularly if it is made from brittle cast iron. This would require a major repair.
So if your indoor temperature is below freezing, it is advisable to thaw and warm the radiators, pipes and the boiler before restarting your system.
The simple way to accomplish this is to use a couple of plug-in heat tracer cables wrapped around the boiler's main piping and pump, plus using a couple of 1500 watt electric space heaters to warm the radiators for about 1/2 - 1 hour each and then relocate the space heaters to direct heat at the base of the boiler.
This solution should suffice to melt the ice within 8 hours. As the water melts it will create a slight convection current that helps spread the heat upwards towards the radiators.
NOTE: the space heaters may need to be plugged into two different electrical outlets or you risk blowing a fuse.
If the system has been exposed to sub-zero temperatures for many days, it can take a day or more to thaw your pipes and warm the water in the system sufficiently using this method. However, it is important to completely thaw the system to avoid thermal shock before you restart the system.
If in doubt, wait longer...
Before proceeding to start the system, you can drain water out of the boiler service drain valve into a bucket. Fluid with NO ice crystals should come out the drain, if you have ice keep warming. If not it should be safe to proceed with start-up.
If you have a thermometer, you can measure the temperature to assure it is over ~40 F or go by your judgement based on feel to bare hand. If it is shockingly cold, its best to warm the system further.
See the image below.
What if your boiler was already set to go on when you left your home for a warmer abode?
So what if you didn't turn down your thermostat before abandoning your home a warmer temporary abode? If at all possible, return home and turn off the system prior to power coming back on!If you can't do that you will have to trust to dumb luck and hope for the best.
But you should take precautions once you return home after the power has been restored, to ascertain that the system hasn't frozen while you were away and that it has started up properly.
NOTE: Use extreme caution, hot water escaping the pressure relief valve can scald instantly!
If the boiler is trying to operate with frozen pipes the boiler will be coming on & off frequently, as in every minute or two. Hot water may also be intermittently released from the boiler's pressure relief valve. Your home will not be heating properly as well.
If you find this is happening, don't panic. The boiler safety switch is turning off the burner before the boiler temperature gets to an unsafe level, typically about 180 F. The limit switch is set well below boiling temperature so that steam should NOT be created that could cause an unsafe internal boiler pressure and an explosion. The pressure relief also prevents unsafe pressure build-up before it can get to an unsafe level as well.
There is a real risk of damage to the boiler heat-exchanger if this abnormal operation is happening though so you should turn the system off and call a service person.
You can also first try the above solution for frozen pipes which is the most likely cause of the improper operation. Turn off the boiler switch or thermostat. Then follow the above procedures. After system is thawed turn it back on and check again.
AGAIN, BE CAREFUL OF EXTREMELY HOT WATER ESCAPING THE PRESSURE RELIEF TUBE.
If the system continues to operate abnormally after this approach call a qualified service technician.
