Central Heating Problems: Fix Them Yourself


Most noises in heating systems can be traced to one of two things:

add descaler or inhibitor to the central heating systemScale build-up on the insides of the pipes and the boiler heat exchanger is particularly common in hard water areas. The symptoms are howling, tapping or banging in the pipes, and roaring (‘kettling’) inside the boiler when it is firing.

Remove the scale by adding de-scaling fluid (available from builder’s and plumber’s merchants) and flushing out the system. Afterwards, add corrosion inhibitor to guard against future build-ups.

1. To add descaler or inhibitor, turn off the water supply at the expansion tank. Open the draincock (see How to Draink a Central Heating System) and draw off three bucketfuls of water . . .

2. open the drain cock, drain 3 bucketfuls and close again. . . then close again. Return to the expansion tank and pour in the relevant fluid folowing the manufacturer’s instructions. Afterwards turn the water supply back on.

Expansion noise is caused by the pipes expanding and rubbing against their brackets or nearby objects as they heat up. It is most noticeable first thing in the morning. The cure is to track down all likely trouble spots and cushion them with foam so that the pipes can’t rub against anything. Check, too, that the brackets are secure.

It’s also possible that the pump — see below — is running too fast or too slow. If yours has a speed setting dial, turn it up or down and see if this helps.



The water level in the expansion tank is the first thing to check in the event of a circulation problem. The minimum depth is 100mm (4") — any less, and the system won’t function to full efficiency.

The drop in level is likely to be due to a stuck ballvalve, in which case wiggle the valve arm to free it.


Pump faults

check the pump is workingThe pump is a metal cased object around 125-150mm (5-6") in diameter, which is usually plumbed into the system near the boiler or hot water cylinder. Check the pump is working with the heating switched ‘on’, and there are no loose wires.

Pumps have a habit of seizing up, particularly if the heating has been off for some time, but many types can be restarted without having to be dismantled.


if the pump has jammedLook for a restart mechanism in the centre of the pump. It may be a screw slot (possibly under a plastic cover), or a small plastic knob. Switch off the power before you begin.

If the pump won’t restart, or it is noisy enough to be heard (indicating wear in the bearings), it must be dismantled and probably replaced.



Airlocks and blockages

Airlocks in pipes tend to affect radiators higher up the system (they are rare in the hot water cylinder pipes). Start at the pump, which has a bleed valve fitted on the side of the casing. Some systems have further bleed valves (aircocks) at strategic points in the pipework.

Sludge blockages produce similar symptoms, but tend to affect pipes lower down the system. Minor blockages can often be shifted by speeding up the pump. If not, drain the system and flush.

check for airlocksCheck for airlocks with the pump switched off. Unscrew the bleed valve a few turns and listen for the tell-tale hiss of air. Close the valve when water appears.



Trade Tip

Shifting pipe airlocks

"If your pump has a speed control, note the setting then turn it up to its highest point. Turn back after a few seconds and repeat at half-minute intervals.

If this doesn’t work, run a hose from a mains-fed cold tap to the system drain cock and get a helper to check the expansion tank. Open the drain cock, then turn on the tap gently so that water flows into the system, pushing the system water (and any air) out via the expansion tank. Turn off the tap as soon as your helper sees the tank begin to overflow."

26. May 2011 by admin
Categories: Heating | Tags: , | Comments Off on Central Heating Problems: Fix Them Yourself


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