Have just moved into new flat, with a gas boiler. Not sure if it's a combi yet.
First weird thing - when I turn on the 'heating' on the wall timer, nothing happens. It only runs when I turn on 'water' also. Does this mean it's a combi boiler?
The pressure gauge was also showing as zero, so I turned the water tap in the emersion cupboard, which fed the boiler, allowed it to start, and set the gauge halfway round the dial.
Went out to the shops and when I returned water was gushing out the side of the flat! Boiler (or pipes above) were making a real racket.
After a bollocking from neighbours, realised I had to turn the water tap off again. Gauge reset to just a few notches above zero, and boiler ran fine.
Is this how it should work? Do I need to feed water into the system now and then manually by opening then closing that valve/tap?
Depends on how the pressure got to zero. If you top it up to say 1 bar and it falls to zero over time *without* the boiler firing up, then you have a leak.
If you watch the pressure when the boiler kicks in you should see it rise as the system warms up. However it should not go above 2 bar typically. If you see it shoot up to say 3.5 bar then chances are the pressure release valve will kick in, vent some water and you will be back to zero again when the syetm cools off. That wouls indicate a faulty pressure vessel.
It could indicate a problem with the pressure vessel - but it may be one which you can fix yourself.
The pressure vessel has a diaphragm inside with (compressible) air on one side and water on the other. If there is insufficient air in it, the water has nowhere to expand to when it gets hot - resulting in the pressure rising too much and the safety valve opening, causing the pressure to drop.
The vessel should have a Schrader valve (like a car type valve) at which you can measure and top up the air pressure. With the water system unpressurised, the air pressure should be about 0.7 bar (~10 PSI). Check it with a car tyre pressure gauge, and top it up with a car tyre pump if necessary. If water comes out of the Schrader valve, the diaphragm is shot and the vessel will need to be replaced. Otherwise, just top it up as necessary.
Then use the filling loop to pressurise the water system to 1 bar when cold. Then, when the system heats up, the pressure should rise to no more than about 2 bar - and certainly not enough to trigger the safety valve, which operates at about 3 bar. When it cools down, it should return to 1 bar.
Can you confirm that this sounds like a combi boiler (or not) given the fact that the radiators will only get warm and the boiler will only start up when I turn the WATER switch on, but nothing happens when I turn the HEATING switch?
The fact that there is a switch for water heating indicates that it is unlikely to be a combi. A combi boiler produces hot water on demand, so is "always on" and requires no switch.
(cont...) So back to my question, why does nothing happen when I flick the HEATING swtich, but the radiators warm up when I flick the WATER switch (both on the wall timer)? :-S
My guess is you have a three port valve that is stuck. It may be a mid position valve, and the valve has been set manually to the mid position (many valves of this type have a leaver on the side that will do this.
(you neglected to mention if the hot water also got heated)
It appears that you may be right. If I move the valve lever to off, then turn the HEAT switch on, the valve lever doesn't return to on. However, it does work the other way automatically. You can hear a click when it doesn't move, indicating the wall timer is sending the correct current.
Is the simple solution a new valve or could this possibly be anything else?
The other strange thing as mentioned in my above post, is that only the WATER switch turns the system on. E.g.: Water off = gas boiler off, valve off, pump off Heat on = nothing Water on = gas boiler on, valve on, pump on, radiators on
Thanks for the excellent info. Have now done all the tests, topped up the pressure from 5 PSI to 10 PSI, topped up the water to 1 bar when cold. When warm it rises to just below 2 bar, *but* when cold again it drops to zero, doesn't remain at 1 bar.
Faulty pressure vessel [re-check to make sure it's *still* at 10psi]
Faulty pressure relief valve [find where it discharges to the outside world, and hang a plastic bag on it to see whether it collects any water when the system is running - it shouldn't!]
Water leak elsewhere [inspect all pipework, junctions, radiator valves, etc.]
It sounds as if you have a Y-Plan system, with a 3-port mid-position motorised valve. Your system is probably wired incorrectly. You can find a wiring diagram in the Y-Plan section of
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particular attention to the connections to the grey wire on the 3-port valve. This needs to be live when HW is either switched off at the programmer or satisfied at the cylinder stat. So there must be a HW-off connection to the programmer, and the cylinder stat must have change-over contacts - with the one connected to valve-grey still live when the water is hot. In this condition, it's the valve which switches the boiler on via the orange wire, but it needs grey to be live to be able to do this.
If the wiring *is* ok, you could have a faulty microswitch inside the valve actuator. It sounds from an earlier post as if the actuator may be suspect, anyway. With most makes of valve you can replace the actuator without disturbing the wet part of the valve.
OK, I just had a look at the install manual for you boiler. Looks like we may be talking at crossed purposes!
You boiler appears to be designed for gravity circulation for the hot water heating (i.e. there is a separate feed and return connection on the boiler for connection to the hot water cylinder). The central heating is handled separately.
With these types of system you don't really get fully independant control of heating and hot water - however it does depend on how it was all plumbed in the first place. Some boilers of this type can be configured to run fully pumped while simply ignoring the gravity circulation. However usually any time the boiler is on there will be heating to the water via non pumped circulation.
This would suggest that your motorised valve will be a two port valve (i.e. only two pipes in and out and not three). Often positioned close to the hot water cylinder. This valve is normally driven from the cylinder stat such that it closes when the cylinder is up to temperature.
You would expect water on to give boiler on, pump off and valve under control of the cylinder stat.
Heating on would give boiler on, pump on (or possibly under control of the room stat), valve under control of cylinder stat.
We need to understand a bit more about how your system is connected up - what pipes go where, and what control wiring there is.
However in the simplest configuration you would only have simple "on" or "off" control of your system (and the fact that the *programmer* can cope with independant water and CH could just be a red herring!). The pump would be controlled by the room stat, the valve by the cylinder stat, and the call for heat signal to the boiler would be generated by the combined outputs of the stats in serise with the timer.
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