Plumbers & electricians in Lee

The northern end, around Lee Green where SE12 meets SE13 and SE3, is the oldest part. Victorian and Edwardian terraces and villas, plenty of them long since split into flats, with back additions that put the kitchen a long way from the front door.

Follow the railway south and it changes completely. Lewisham Council built its Grove Park estate over forty odd acres in the late nineteen twenties, a cottage suburb of bay fronted semis laid out around greens. Horn Park went up on old farmland from the nineteen thirties and was not finished until the fifties, the war having got in the way. The Chinbrook estate is later again, planned by the London County Council in the early sixties.

What all of it shares is that the heating was retrofitted. Every condensing boiler here went into a house whose drainage was finished decades before it arrived, and whoever fitted it had to find somewhere for the condensate to go.

Why the boiler stops on the coldest morning in Lee

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A condensing boiler turns part of the flue gas back into water, and that water is mildly acidic and has to drain away. The proper place for it is an internal waste or soil pipe, and in plenty of Lee houses there was nothing suitable in reach. The boiler went into a kitchen at the back of a Victorian addition, a Grove Park landing cupboard or a converted upstairs bathroom, so the shortest route was out through the wall in thin white overflow pipe and down to a gully. That pipe never carries a steady flow. It takes small slugs of warm water and sits cold and empty in between, which is why a day or two below freezing closes the bore with ice.

What you notice is that heating and hot water were fine at bedtime and dead by morning, always on the coldest night rather than the wettest. The boiler tries to fire, there is a gurgling from inside it as the condensate backs up behind the ice, then it locks out and shows a fault code. The code differs by make, so read what your own manual calls it, because a condensate lockout is a safety feature working correctly and not a broken appliance. Where the outside pipe can be reached safely, warm water poured slowly along it, or a cloth wrung out in hot water held on the elbow, usually clears it. Never boiling water onto cold plastic, and never a flame.

The permanent answer is not lagging on its own. Insulation slows a pipe losing heat, it does not put heat into it, so a thin outside pipe holding a few millilitres of standing water still freezes in a long cold spell however neatly it has been wrapped. The real fix is to shorten the problem. Rerouting the condensate into an internal waste, so that nothing runs outside at all, is right wherever the drainage allows it. Where it has to stay outside, that means upsizing the external section, cutting out long runs and needless bends, giving it a continuous fall, and only then insulating. A thermostatic trace heater is a fair last resort for a run that cannot be moved. Which one applies depends on the house, and in a first floor flat with no reachable stack the answer can be nothing like next door’s.