Starting Up your Condensing Boiler after the Summer

Modern boilers are very efficient but compared with old system boilers they are very complicated. People usually experience difficulty in starting them up after the summer. You switch the central heating on and nothing happens. What should you do? What follows is for knowledgeable people who are comfortable working with do it yourself projects. If you have any doubt whatsoever call a Gas Safe qualified plumber.

Most modern boilers will only work if the pressure in the central heating system is sufficient. Most boilers need to have a pressure in the system of over 1 bar. Your boilers instructions will specify the pressure that yours must have. First check the pressure gauge on the heating system. If the pressure is low you will need to re-pressurise the system. Somewhere close to the gauge you will see a flexible steel pipe which is supposed to be kept disconnected unless you are re-pressurising the system but you will usually find connected. At one end of this flexible steel pipe is a valve (or tap). If you turn this on you should see the gauge indicate that pressure is rising, some boilers have a digital pressure reading on the boiler. When the pressure reaches just over 1 bar (or the level recommended by the manufacturer in its instruction book) turn off the tap and disconnect the pipe.

In some systems there is a second valve that also needs to be opened. Remember after re-pressurising the system turn off all valves and do not over pressurise the system. You should find the heating works. If you find you have cooler parts at the top of your radiators, this will be air and needs to be bled, check all your radiators for air starting at the bottom radiators and working your way up bleeding as you go. You may have to re-pressurise the system after, but after that the heating should work properly.

Systems can lose a little pressure from time to time but if you find that you have had to bleed extensively or the pressure repeatedly drops so that you have to re-pressurise frequently then it is a sign that there are leaks or weeps in your pipes or radiators. Leaks and weeps are commonly found where the radiators are linked to the heating pipes. Over periods of time the expansion and contraction of the copper and steel radiators often creates tiny leaks. You may not see them because the heat from the radiator may evaporate the water but they will be there. In this case you need a qualified plumber to attend to this. He or she may need to replace radiators and may find other leaks in the system.

That would be money well spent. Leaking systems means re-filling with raw water; this causes more oxygen in the system and dilutes the inhibitor, this can lead to corrosion and an inefficient system costing you more gas as well as the problems of living in an unheated home in cold weather.

If you have a condensing boiler, check the route of your condense pipe, if it runs externally, either get an installer to re-route the pipe internally if possible, or increase the pipe size externally and heavily insulate, or even add trace heating if the pipe is very exposed, these preventative measures will prevent your condense freezing in the coldest weather as we saw earlier in the year ensuring your boiler works and you have heat when you most need it. You can get more information on boilers in freezing conditions at

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