DIY Heating Plumbing Tips 5 - Looks at some of the common problems associated with hydronic central heating systems.
Below is a list of what's on this page:
This is because the boiler is possibly overheating, and this may be caused by:
The picture below indicates the areas of accumulated sludge in a central heating system.
Solution - Power Flushing, Power Flush the heating system and treat with a descaler and corrosion inhibitor.
Solution - Have the chimney swept to remove and clear away the heavy soot.
- Turn the boiler off and allow the system to cool down. Most boilers have a 'pump overrun' feature, this simply means that the water 'circulating pump' will continue to circulate the heated water around the system for a few minutes after the boiler has been shut off.
This is to help cool down the water in the boiler's heat exchanger. When the system has cooled down try operating the thermostat for the boiler, if no clicking sound can be heard then there is a problem with the thermostat, and you will need to call a heating engineer.
Many of the new boilers have an onboard management system and will display an error code if a problem is detected. Refer to the boiler's user manual for error code definition and solution.
If you can hear the thermostat click when operated then you may just need to reset it to a lower temperature.
It is a better practice however, to have the boiler 'interlocked'. This is a wiring arrangement that only allows the boiler to fire-up if there is a demand for space heating from the room thermostat, or a demand for hot water from the hot water cylinder thermostat.
Interlocking the boiler completely prevents 'boiler short cycling', the unnecessary firing-up of the boiler when there is no demand for space heating or hot water.
- With the older traditional boilers the pump is installed separately on the heating circuit and not within the boiler, unlike the new system boilers where the pump is now part of the boiler.
Check that the pump is running, if not, switch off power and check the wiring connection. If the pump is running but the pipe on the pump outlet side is cool, then there may be an air-lock.
Switched off the pump and unscrew the the bleed screw on the center of the pump face plate to remove any trapped air, tighten up screw when water starts to come out.
If the pump is still not working close off the isolating valves on either side of the pump and remove the pump. Check for blockages like the build-up of black sludge within the pump and clean, or if need be, replace the pump.
- In open vented systems check the feed & expansion tank. If empty then there may be a problem with the 'ball float valve', it may be stuck. Try moving the the float arm up and down to free it and to restore the flow.
Check that the mains water supply to the feed & expansion tank has not been turned off. Check that there are no frozen pipes.
With sealed heating systems check the water pressure, there should be at least 1 bar (100 Kpa) of pressure when the system is cold. If the pressure gauge reads less than 1 bar, connect the water 'filling-loop' for the heating circuit and top up (the pressure gauge may be located on the boiler or connected to the pipework on the primary circuit).
The boiler may not be working for a number of reasons:
- Check fuel storage or mains supply. check that the main fuel supply valve has not been turned off.
- If the boiler has a permanent pilot light and it has gone out, try re-lighting the pilot light by following the manufacturers instructions. The re-lighting instruction is generally written on the back of the boiler's front panel.
If the pilot light fails to ignite it may be faulty and need to be replaced. Turn off the gas supply to the boiler and call a central heating gas engineer.
Most new gas-fired boilers no longer have a permanent pilot light, instead they have a electronic pilot ignition - meaning that the pilot only comes on and lights the burner when there is a demand for heating or hot water. Refer to the user manual for definition of error code - if it's an ignition fault call a central heating gas engineer..
- Check that the timer and/or programmer is turned on and that the heating times are set correctly. If it is switched on and correctly set then it may be faulty and needs to be replaced.
- Check that the room thermostat, the hot water cylinder's thermostat and the boiler's thermostat are not set too low. The boiler will not fire-up if the is no heating demand from any of the thermostats.
If the boiler is working but the radiators remain cool then it is probably a problem with the.
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- Check and adjust if needed the the setting on the thermostat/programmer or timer. Switch off the electrical power if the pimp is still not working and check the wiring for any loose connections. If the wiring looks in good order but the pump still fails to work you will have to call a heating engineer.
When there is a demand for heating or hot water the thermostats, either the room thermostat or the hot water cylinder's thermostat will firstly switch the motorized valve(s) to heating or hot water, then turn on the circulating pump, and then finally, switch the boiler on.
This could be because there is a problem with:
- Switch off the electrical power to the boiler and drain the heating circuit, then remove and replace the motorized valve.
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A radiator may not heat up because:
- Check that the radiator's handwheel valve is open. turning the handwheel valve in an anti-clockwise direction will open the valve, fully turning it in a clockwise direction will close the valve.
- Check the valve is turned on and not set too low. If the radiator still does not heat up, close the the valve and remove the head and check that the plunger pin moves freely.
If there is a problem with the thermostatic radiator valve, the system will have to be drained and the valve replaced.
- Remove the cover cap on the lockshield valve and release the locking nut around the valve shank, turn shank in a anti-clockwise direction, to open use a screwdriver or spanner.
Some types of lockshield valves are operated (open and closed) with a special key.
Power Flushing, Power Flush the heating system and treat with a descaler and corrosion inhibitor.
The reason a radiator remains cool at the top while the bottom is warm is because there is:
- Bleed the radiator. To bleed a radiator turn off the heating system and wait for the circulating pump to stop running. Open the bleed valve which is located at one of the top ends of the radiator with special bleed valve key. Close the valve after the air has been released from the radiator and the water begins to come out. Catch water in bowl.
The reason why the center (and bottom) of the radiator is cool while the top and the ends are warm is because:
- Power Flushing, Power Flush the heating system and treat with a descaler and corrosion inhibitor.
If the overflow pipe from the feed & expansion cistern/tank is continually dripping it could be due to:
- Close off water supply to feed & expansion tank and bale out the water to a level below the valve, then remove the ball valve and check the washer. If the washer is no longer seating correctly replace it with a new one.
- Bale out the water in the feed & expansion tank to below the valve level and then unscrew the 'ball float' from the 'float arm' and fit a new 'ball float'.
- Replace hot water cylinder if coil cannot be easily repaired or replaced.
If the coil is split, then the overflow pipe in the feed & expansion (F & E) tank will only drip if the F & E tank is positioned below the cold water storage cistern (CWSC) and therefore exerts less static pressure (head) than the CWSC.
To test this (if possible), turn off the boiler and close off the water supply to both the cold water storage cistern and the f & e tank, and allow the system to cool down. Measure the water level in both cisterns using a dip-stick, do not use water overnight.
Take another measurement the next day, and if the water level in the f & e tank has`increased and the water level in the cold water storage cistern has decreased, then the coil most probably has a leak. You will need to call in an heating engineer to further test the system.
Water may be leaking from pipe`connections:
- Turn off the boiler and then tighten up the leaking joints.
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Thanks for the advice for removing an air lock from an indirect system. Had to change an inlet on my cistern. First time I have tried any home plumbing. After draining the cold tank system air locked when I refilled the tank. Garden hose and mains pressure up the tap sorted my problems. Would not have known what to do without the advice on the site. Many thanks Sean United Kingdom.
An excellent site. I have found it very usefull. I am currently in the design phase of a new house and have be pondering which heat system to use. From your site I have been able to choose the right system. Ross New Zealand
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