I wrote recently about why your condensing boiler may suddenly stop working in very cold weather, and it has proved to be very popular. I asked our Genersys engineer, Chris Flaherty, what is a common problem this time of the year and he explained that you may suddenly experience loss or hot water or loss of heat in the radiators. Your gas boiler still seems to be working but the heat from one source or the other is not. What has happened?
Well, gas boiler can fail for a variety of reasons but in an emergency before you call the engineer to fix it, it is worth looking at the three port diverter valve. A gas boiler heats water and heats radiators by heating an exchange fluid (water with corrosion inhibitors) and diverting the heat through a sealed circuit either into the cylinder or into the radiators or both. The device that does this diversion is called a diverter valve, or a three port valve. Sensors tell the valve when to switch the heat from the hot water to the radiators and when to direct heat to both places.
Like any part of a heating system over time the diverter valve may fail, and get stuck. If it gets stuck in the radiator position, the boiler will only provide space heat, and no hot water. If it gets stuck in the hot water position it will only be provided and there will be no space heating.
If you find this happens at home a quick and simple way to temporarily fix the problem is to locate the three port diverter valve. I have attached a picture of the Honeywell model, which is very popular, but all models look very similar and have similar features.
You will see a slide switch; this enables you to lock the diverter valve into a position where the boiler will heat the radiators as well as the hot water, by pulling the switch into its locked manual position- there is a small place that keep the switch (and therefore the valve) in this position. That should keep you going until you can get an engineer to replace to fix the valve, so it operates as it should.
I stress that this fix should only keep you going until you get the plumber to call; keeping the valve in this position prevents the boiler from being controlled as it should be regulated.
Of course prevention is better than cure, so while you are feeling energetic, ensure that the pipe work in the loft and the storage tanks in the loft, if you have one, are well insulated, to protect them from freezing in these cold snaps,
It is also a good idea to know where your stopcock is and from time to time check that it is working; plumbing emergencies are bad enough without not knowing how to turn off the mains water, which might be leaking all over the home from a burst pipe.