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Boiler losing water pressure
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Oddly the pressure is now showing 1.4/1.5 without a top up, rising to 2.0 when running/warming the house, so weird how it was 0.9 this morning then back up again! Is topping up quite normal at least a couple of times a year?
Just in case, where is the expansion vessel located?
Is topping up quite normal at least a couple of times a year?
In theory no.
The systems are, or should be, totally sealed.
If the system has been designed and fitted correctly, inhibitor checked and maintained at the correct strength, (see (1) below), if the integrity of all joints, PRV's, etc. are 100 % there should be no pressure drop at all.
However systems are not always 100% leak proof, though they should be, so a small leak, or several small leaks will drop pressure over time due to water loss. ( see (1) below )
The other reason for pressure loss is a loss of air pressure within the pressure vessel, in most instances this is easily corrected by restoring the pressure vessel base pressure back to .5 bar by pumping air into the pressure valve via the schrader valve. A simple task performed with a bike pump but occasionally a bit of a struggle due to location. This can be quite a good earner for dishonest plumbers as an easy way to condemn a boiler. :eek:
(1) Easy to forget that every time water is introduced to bring the pressure back to normal, the inhibitor is being diluted, therefore if there is a need to constantly correct the pressure, the ideal situation is to correct the leak, either by remaking the joint etc. or if a small invisible weep, ie. under floorboards, to use a propriety CH leak sealant, then get the inhibitor back up to the correct level.0 -
Just wondering if you have set the pressure slightly too high at 1.5bar ?
Not sure, just going off the notice on the front of the boiler which states top it up to 1.5. I suspect if I only topped it up 1 it would be cutting out all the time, as the cut off seems to be 0.9.
Also I have to turn two levers to increase the pressure, not sure if both of them are suppose to be closed or not?0 -
Spoke to my neighbour about the boiler and they have had the same issue. The boiler man came out and simply used a foot pump to blow some air into a valve/bag/balloon type thing in the top of the boiler. Any ideas what that might be?0
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Not sure, just going off the notice on the front of the boiler which states top it up to 1.5. I suspect if I only topped it up 1 it would be cutting out all the time, as the cut off seems to be 0.9.
There are variations, the 1bar I quoted is an average figure, but as always go by the manufacturers figures, which in your case appears to be 1.5bar.
The ideal conditions for setting the pressure are when the CH system is cold and the boiler hasn't been used for an hour or two.
Also I have to turn two levers to increase the pressure, not sure if both of them are suppose to be closed or not?
That's correct, there should be one from the mains cold water pipe to the filling loop and one from the filling loop to the system.
Both should be closed when the required pressure is achieved.0 -
Spoke to my neighbour about the boiler and they have had the same issue. The boiler man came out and simply used a foot pump to blow some air into a valve/bag/balloon type thing in the top of the boiler. Any ideas what that might be?
He has repressurised the expansion vessel.No free lunch, and no free laptop0 -
Spoke to my neighbour about the boiler and they have had the same issue. The boiler man came out and simply used a foot pump to blow some air into a valve/bag/balloon type thing in the top of the boiler. Any ideas what that might be?
That is the pressure, or sometimes called, expansion vessel, made in most instances of steel.
Why it it needed ?
As mentioned previously, when water is heated it takes up a greater volume (expands), in a sealed system this extra volume has to be accommodated, also when pressure is applied to a sealed system used to heat water, think also of a car radiator or pressure cooker, it allows the water to be raised to higher temperature, the water doesn't physically boil and it prevents steam bubbles and steam pockets being formed at hot spots.
How is it done ?
Actually the expansion vessel is one of the simpler bits of a boiler, there are several different shapes, all work the same.
Imagine a sealed ball inside halfway down is a rubber diaphragm which seals and separates the upper and lower chambers.
There is a schrader valve, exactly the same as a car tyre valve in the upper chamber (air).
There is a pipe connecting the bottom chamber (water) to the CH system.
The vessel has an initial air charge, when new, of on average .5bar, this is achieved by connecting a bike or car tyre pump to the schrader valve and pumping it up to the required initial pressure.
In doing this the rubber diaphragm is pushed into the lower (water) side.
When filling the boiler to the correct pressure the diaphragm is pushed towards the air side until the correct pressure is achieved, though there is still ample space for the expanded water.
When the water is heated, it expands, pushing the diaphragm towards the air side, compressing the air to the higher value you see on the gauge.
The reverse happens when it cools.
Favorite faults.
1) Loss of air pressure via the shrader valve, cure pump it back up, your neighbours problem.
2) Split diaphragm, cure replace or an external one fitted.
3) Corroded / rusted vessel, cure replace.
4) An odd one which can cause head scratching and unnecessarily condemned boilers, the pipe (water) between the vessel and system gets blocked.
Any danger with insufficient or excess pressure ?
There shouldn't be, the boiler should fail to fire, or shut down in the event of insufficient pressure, though the boiler may make some odd noises.
With excessive pressure the PRV should open to safely vent the excess outside with eventually the overheat sensor shutting down the boiler.
Hope this helps.0 -
I had a similar problem with my old boiler. I noticed that the pressure was being lost when hot water was being used.
Turned out to be something 2 boiler guys including a mate had never seen before, which was there was a split in the coil in the hot water cylinder. So as the hot water is used from the cylinder it was dragging water through the split from the Central heating system.
Neil0 -
There is one other option that has not been mention and that is the pressure sensor can get clogged and give false readings resulting in premature lock out as a false low pressure reading is given.
If your boiler has a digital readout for the pressure this is also false in this instance.
A proper diagnostic of the fault can only be in conjunction with access and PROPER fault finding techniques and checks of all the operational components involved by a PROPERLY experienced and qualified engineer.
It should also be noted that the filling loop should legislatively be disconnected when not in use to conform to Water Bylaws, to prevent the water mains from contamination by the heating system water, although double check valves are used on more modern systems there are bugs that can flow upstream of opened water valves?Signature removed0 -
There is one other option that has not been mention and that is the pressure sensor can get clogged and give false readings resulting in premature lock out as a false low pressure reading is given.
If your boiler has a digital readout for the pressure this is also false in this instance.
A proper diagnostic of the fault can only be in conjunction with access and PROPER fault finding techniques and checks of all the operational components involved by a PROPERLY experienced and qualified engineer.
It should also be noted that the filling loop should legislatively be disconnected when not in use to conform to Water Bylaws, to prevent the water mains from contamination by the heating system water, although double check valves are used on more modern systems there are bugs that can flow upstream of opened water valves?
There are boilers with no 'filling loop' as such, the valve is part of the boiler, connected to the cold inlet, therefore can not be removed / disconnected.0 -
And dont that make ya wonder exactly what engineers who design combi boilers actually know about the associated legislationsSignature removed0
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