Simple explanations for plumbing problems

What does 00 mean on a boiler

00 fault on Ideal logic
00 fault on Ideal logic

What does 00 mean on a boiler?

An 00 fault on an Ideal Logic isn’t a true fault but it’s still a problem I’ve been requested to fix.

OO is displayed on the front of an Ideal Logic boiler when there is no demand. For a combi boiler that is:

  • Room thermostat set too low
  • Heating timer turned off
  • Summer winter selector switch turned to summer
  • No hot water demand.

Why have I got a 00 fault?

Room thermostat set too low:

The heating will only come on if the room thermostat is set above the current room temperature (a demand).

If you always keep your room thermostat at 20oC and the room temperature is 23oC (for example in the summer or if the heating has been running for a long time) the heating will not turn on. As soon as the room temperature drops to below 20oC there will be a demand and the heating will operate.

Room thermostat set at 30oC
Room thermostat set at 30oC

The thermostat in the picture above is set at 30oC so the heating will operate until the room is above that temperature.

Room thermostat set at 10oC
Room thermostat set at 10oC

The thermostat in the picture above is set at 10oC so the heating will not operate until the room is below that temperature. As the temperature is set very low the heating will only very rarely come on. This is the type of situation where 00 would be displayed on the boiler.

Beware that not all thermostats look like this. Some are digital, some have dials that turn in the other direction and others are a mixture of timer and thermostat.

Your thermostat may have a battery in it that can run out. If you aren’t sure a wireless battery powered thermostat always has a receiver in the boiler or on the wall near the boiler. Check to see if there is a battery compartment on the wall thermostat and replace the batteries.

Heating timer turned off

In order for the heating to work the thermostat must be turned up and the timer must be turned on.

An example of a mechanical timer
An example of a mechanical timer

The picture above is of a mechanical timer (from an Ideal Logic) that is turned to constantly on.

The circular switch at about 9 o clock can be moved up and down to select: always off, timer or always on. The selector switch is currently set to always on. If the round switch was pushed up the heating would never come on. If the switch was moved to the middle it would only come on at the times set on the timer.

Summer winter selector switch turned to summer

Ideal Logic boilers have a power selector switch with three options.Boiler off far left, hot water only in the middle and heating and hot water on far right. This is a throwback to when thermostats and timers were not as common. In the summer you would turn the heating off at the boiler. In the winter you would turn it back on again at the boiler.

Hot water only mode will create a 00 fault on an ideal logic when using the heating
Hot water only mode will create a 00 fault on an ideal logic when using the heating

When you have the switch set to hot water only the heating will not work. The thermostat and timer are disabled so turning them up or down will have no effect.

No hot water demand

Inside the boiler there is a small propeller (flow turbine) that turns when water flows through the boiler to the hot tap. This is how the boiler knows that hot water is required.

If the water is flowing too slow the boiler will not recognise the demand and will not fire.

If the water flow turbine is broken or clogged then it cannot turn and the boiler will not fire.


If an 00 fault is displayed on your Ideal Logic turn up the thermostat, turn on any timers or run a hot tap.

If the boiler still doesn’t turn on you’ll need to get a gas engineer or electrician to check you boiler or controls.

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Filling loop left open

After use the valves on the filling loop should be closed, the metal braided filling loop removed and the valves capped.  The majority of people don’t do this so there is always a chance that the valves can be opened accidentally or be faulty.  This can allow too much pressure to develop in the system which may cause the metal pipe near the boiler to overflow.

The first step is to turn the taps so they are in the off position. If its a round tap turn it clockwise.  If it has a lever turn it so that is not in line and at 90 degrees with the body of the valve.  If it has been accidentally turned on you will hear the water flowing and hear the flow stop when you turn the valve to the correct position.

The filling loop below is open


The filling loop below is closed


It doesn’t need to be as pronounced as this to cause the pressure to go up, even slightly open is enough.

To fix this you need to turn both valves (or one if you only have one) off. This should make the metal pipe outside stop overflowing.

The metal overflow pipe should only overflow if the pressure is above 3. So when the pressure goes back down below 3 the water should stop.

If it doesn’t then you might need a new safety valve as they are notorious for not resealing after they have opened. This is a job for a gas safe engineer not DIY.

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When a leaking radiator drops pressure.

The pressure on the customers boiler had been gradually dropping over several months. As the drop was so slow it couldn’t be a massive leak. She showed me a radiator that had a rusty mark around one of the plugs at the top. This was more than likely the culprit.

Although there was no drip of water or any marks on the floor underneath it did feel wet to touch. Over several months this is enough to drop the pressure so it has to be changed.

The process of changing this plug is pretty simple. You can find a replacement plug on this link.

Turn off the valves, bleed the pressure out of the isolated radiator then take the plug out.

The valves were both lock shield types so I closed them with my tiny pump pliers.

Then I bled the excess pressure from the bleed point catching the dirty water in some blue roll.

When the water stops coming from the bleed point you can be pretty confident the pressure is gone.

Next unwind the plug from the radiator. I like to use pump pliers as they give a better grip. However they chew the fittings up. If they are on show or decorative you need to be more careful.

Some water will always leak out when you are repairing a leaking radiator. It's important to catch as much as possible.

Even though the pressure is gone a fair amount of water still comes out when the plug is removed. Have plenty of blue roll and a tray ready to catch it. I’ve got an old plastic tray that I’ve had for years but when it eventually gets broken I’ll replace it with a Plumb Tub to make life easier. Dirty central heating water can easily stain light coloured carpets make sure you have everything in place before you start.

Some water will always leak out when you are repairing a leaking radiator. It's important to catch as much as possible.

When the plug is removed clean the inside of the threads to remove any old sealant and dirt. Then refit the replacement plug. Use a flat spanner (I use an adjustable) to refit it. This saves the chrome from being chewed up.

Reopen the valves and check for leaks. If you have a pressurised system check the pressure gauge. Top up if necessary.

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