Plumbers & electricians in Tonbridge

Tonbridge grew up where the Medway could be forded, on a spur of firmer ground above a marshy river, and the castle Richard Fitz Gilbert raised there in the eleventh century still stands over the water with its great gatehouse. The High Street runs for about a mile through the centre. When the railway arrived in eighteen forty two the town filled in behind it, and the Victorian railway terraces around Douglas Road and Barden Park on the south side are the result, with Vauxhall to the south east and later estates laid out on the Radburn pattern to the south west.

The river still sets the terms. The flood of nineteen sixty eight was bad enough that the Leigh Barrier was built upstream, completed in nineteen eighty one, to hold the Medway back across a flood storage area before it reaches the town, and a new defence went in along Avebury Avenue after the floods of the winter of two thousand and thirteen.

Plenty of these terraces started out with a tank in the loft. Plenty now run a sealed combi or system boiler instead.

Falling boiler pressure in Tonbridge houses

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A sealed heating circuit is filled from the mains through a filling loop, usually to somewhere around one to one and a half bar on the gauge when everything is cold, and then closed off. Water expands as it warms, and in a sealed loop that growth has to be absorbed somewhere, so every combi and system boiler carries an expansion vessel: a steel shell split in two by a rubber diaphragm, with water on one side and a charge of air or nitrogen on the other. As the radiators heat, water pushes into the vessel and squeezes the gas, and the gauge rises a little and settles. Over the years that charge seeps away through its valve, or the diaphragm perishes and splits, and the cushion is gone. Now the heated water has nowhere to go except up in pressure. The gauge climbs towards three bar, the pressure relief valve opens at three bar as it is designed to, and water is dumped out through a small copper discharge pipe that runs through the outside wall, normally turned down against the brickwork. When the heating goes off and the water cools, there is less of it in the circuit than there was, so the gauge falls below one bar and the boiler locks out on low pressure. Someone tops it up at the loop, and the next heating cycle throws the extra water straight back out.

In practice it becomes a routine: a gauge that climbs with the heating, sits lower every morning, and a filling loop used weekly.

Look outside first. A drip, or a pale or greenish stain on the wall under that little pipe, means the relief valve has been lifting, and that points at the vessel before it points at a leak. The vessel is checked with the boiler drained down to zero on the heating side, by putting a gauge on its valve and reading the charge, then pumping it back to the figure the manufacturer gives. If it will not hold, the diaphragm has gone and the vessel is replaced. On some combis it sits behind the boiler and means taking the boiler off the wall, and on those a separate vessel on the circuit is sometimes the more sensible answer, which depends on the boiler. A relief valve that has lifted many times often will not seat cleanly again and drips on regardless, so that is renewed too. Only when the vessel holds its charge, the discharge pipe stays dry and the pressure still falls is it a genuine leak, and finding one under a floor is its own job, covered in the post on a burst pipe under the floor. And the filling loop is disconnected after every use, because the water regulations will not have heating water able to find its way back into the drinking supply.