I have an Oil fired boiler central heating system.
Basically it is not switching off based on the timer nor is it being limited by the thermostat. Therefore we are getting very hot all the time ! The radiators are red hot.
The only way to stop the boiler coming on is to turn it off at the power supply.
The boiler does come on & off intermitently but I am guessing that it is being limited by some heat sensor/safety limiter within the boiler.
It may be winter outside but you need shorts & T-shirt in my house.
Also my immersion tank cannot be switched on to heat electrically as it blows the main fuse. No idea if this is connected.
Yes the boiler has a thermostat which regulates the temperature of the water it circulates through the system, so the boiler will come on and off to maintain this temperature. In the short term you can turn down the 'stat on the boiler (maybe behind the front panel, but you shouldn't need to unscrew anything to get at it) to lower the temperature and manually regulate the heating through the rads.
Not the electric bit - sounds as if your immersion heater has failed. But is the boiler heating the water in the cylinder? Is it being asked to via the programmer? What happens if you set the programmer to NOT try to heat the cylinder from the boiler? Does the boiler stop heating the rads then?
My guess is that the valve which directs hot water from the boiler to the cylinder to heat your hot tap water is not working so the boiler keeps going trying to heat the cylinder but the hot water is going round the radiators instead.
Check what sort of valve you have - see
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Is the repair a DIY job or professional ?
If you can suss out the problem and, if the valve has failed, replace pipework and electrics you can do it yourself. It's not the simplest job especially if the pipework is hard to get at and/or the CH wiring is a rat's nest stuffed into a junction box rather than a nicely laid out wiring centre. If you're not reasonably clued-up and experienced in these matters you may be better off getting in a pro (though beware, some pros have difficulty with dodgy wiring systems - you're certainly looking more for a "plumbing and heating" engineer than a general plumber.)
The fault with the immersion heater is unlikely to be connected with the CH being on all the time.
Does the oil-fired boiler normally heat the HW in addition to the CH? If so, is this part working - heating the water to the correct temperature without getting too hot?
Do you have any motorised valves which direct the water from the boiler to the HW cylinder and radiators? If so, how many and what type (2-port or
3-port)?
One possibility is that you've got an S-Plan system which uses two 2-port valves - one for the HW and one for the CH. The HW valve is controlled by the programmer and cylinder stat. The CH valve is controlled by the programmer and room stat. Both valves have separate switch contacts in their motor housings which close when the valves open, and switch on the boiler and pump.
If one of these valves sticks open, it continues to tell the boiler and pump to run - regardless of what the programmer and stat are doing - which would seem to fit your symptoms. The remedy depends on *why* it is staying open. It could simply be a broken return spring in the actuator - in which case it should be possible to replace the actuator without braking into the 'wet' part of the system. If the valve itself has seized, it will have to be replaced - which *does* involve draining the system, unless you can free it simply by rotating its shaft to and fro (with the actuator removed).
We had a fault that sounds similar to yours. Turned out that the mororised valve for the CH had jammed in the on position hence electricity continued to be supplied to the boiler, which of course kept on going even though the times had passed the switch off time.
It wasn't necessary to change the valve, I simply drained down the system , partially dismantled and cleaned the valve and it's been OK ever since.
How can I test if it is a broken return spring in the actuator ? You say simply but does not sound simple to a man of my knowledge !
Is your advice to remove the actuator and try to turn the valve - not that I actailly know how to do that but am prepared to give it a go if you say its easy.
Several of the replies are focusing on the Actuator/valve not working so that seems to be emerging as a strong possibility.
You say 'simply' - was it really easy bearing in mind tht Im an accountant not a plumber ! I will give it a go but is a little scary fiddling with the system in the middle of the winter.
Have as suggested turned down the big green temperature knob on the front.
I am getting hot water but not as hot as usual. I have not yet tried turning off the water heating during the time when it should be heating it. I do not know if it is heating the hot water when the boiler is running without the programmer requiring it- it not as obvious as the rads !
Honeywell V4043H1056 - like the silver box in the web site link. There are two of them. They have a sort of metal stick/switch on them.
There are 3 basic things which could be wrong with the valve and /or actuator - so you need to test for each in turn.
The valve could be opening and closing ok, but its secondary contacts could be welded together - switching the boiler permanently on. This is the least likely, so we'll eliminate that first.
See
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for a picture of the valve. When the valve is closed (which it should be when the heating is supposed to be off) the lever will be in the position shown. You should be able to move it to the other end, to open the valve manually. You will only be able to move it slowly, and will hear the internal gears whirring as you do so. If the lever moves freely to the end without resistance or whirring, and just flops about, this indicates that the valve is remaining open. If the valve *can* be opened with the lever, and closes again when you let go of the lever, then it is the contacts which are faulty - but I don't think this is the case, because it doen't really fit your symptoms.
Assuming that the valve *is* staying open, it can be for either of two reasons. Either the mechanical 'wet' part of the valve is seized, or the return spring in the actuator has failed. To find out which, you need to remove the actuator from the valve. I'm not totally sure how this comes off (mine's a Danfoss!) but there are probably 2 screws going upwards through the baseplate into the bottom of the actuator. Remove the screws and lift the actuator off the valve proper. If the return spring is ok, the actuator will immediately return to the 'valve closed' position - in which case the lever should then operate in the proper fashion. If the actuator doesn't move when it's no longer constrained by the valve, the fault is in the actuator - probably the return spring. In this case, you'll need to get a new actuator.
Assuming the actuator is ok, look carefully at the valve now that the actuator is removed. There is a round shaft with a flat on it - making it like a D in cross-section. It is this shaft which is rotated by the actuator to open and close the valve. You should be able to rotate the shaft through
90 degrees with finger and thumb - or, at any rate, using *light* pressure with a pair of pliers. If it's too stiff to move, that's your problem! Use a bit more pressure with your pliers, and try to rotate it backwards and forwards. [If you observe the D-shaped hole in the bottom of the actuator, when you operate the lever manually, you'll see in which direction the shaft needs to point in the open and closed positions]. With a bit of luck, you'll manage to free it up such that when you fix the actuator back on, it will open and close properly. If not, the wet part part of the valve will need to be replaced which - from what you say - probably means that you'll want to find a plumber rather than DIY-ing it.
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