Hi. Currently experiencing an issue with our oil fired central heating system. When CH/HW is switched on, the central heating does not always work - the hot water does however without fail. We had the timer set to come on last night but alas, only the H/W came on. After a couple of hours of playing with the controls - we could not get the central heating to work at all. This morning however, both worked - quite strange! Furthermore, sometimes when the C/H does work, only half of the radiators in the house heat up - when this happens, we turn the CH / HW off and then back on again immediately and hey presto - those radiators then start to work. Wondering what might be causing this issue. The controls are quite old (Honeywell st6200a) so might need to be replaced, but I'm convinced that there's something else that's not quite right... any advice would be much appreciated
Oil fired central heating issue
- Thread starter CMcN
- Start date
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If the boiler is making hot water for both the Ch and HW store then its working...so you are left with the diverter valve, pump and the controls for it. I would suggest that the controller is not doing its job, that could be a controller fault or a wiring fault. However the first thing I would check is that the unit is actually attached properly to the back plate, are the screws tight. That unit has a set of pins that engage with wiring in a connection box. Over time the box gets a bit loose from the wall and hey presto a dodgy connection.
If you have a meter and know how to use it check the wiring centre for voltages in the various modes. CH on, Hw On, then timed etc etc.
If you have a meter and know how to use it check the wiring centre for voltages in the various modes. CH on, Hw On, then timed etc etc.
Could be an airlock or a crud build up..check the header tank is filling , add some cleaner and inhibitor, bleed the rads could also be the programmer not firing the diverter valve properly...
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I also have oil heating, and have had a similar issue in the past - hot water working, but when it changes to heating, although the light on the control unit shows the heating is on, nothing is happening.
I think in my case it's a microswitch in the valve, not quite connecting/disconnecting when the water goes off. I found it could fiddle with the valve and a small "button" on the side and there'd be a click and I'd hear the valve move, and the heating would come on. For the last couple of years I haven't had the issue. Perhaps your valve is not moving across fully and restricting flow to the rads.
Good luck.
I think in my case it's a microswitch in the valve, not quite connecting/disconnecting when the water goes off. I found it could fiddle with the valve and a small "button" on the side and there'd be a click and I'd hear the valve move, and the heating would come on. For the last couple of years I haven't had the issue. Perhaps your valve is not moving across fully and restricting flow to the rads.
Good luck.
In my set up it's just next to the pump in the airing cupboard. It's a Drayton ZA5 (i think). Its the motorized valve that directs the hot water from the pump either into the radiators or into the heating coil in the hot water tank.
The microswitch would be my first port of call. The microswitch is fitted inside a motorised valve. When the controls wind open the valve, it presses on the microswitch which in turn operates and starts the boiler.
Some systems may have 2-Port valves (I think a ZA5 is an actuator for this type of valve) usually there are two valves, one for HW and one for CH. If the microswitch in the CH valve fails the valve will open but the boiler won't start until the HW valve opens and its switch starts the boiler. At this point water will also flow through the already open CH motorised valve and the radiators will heat up too.
If instead you just have one 3-Port diverter valve there is still a microswitch inside that is triggered when the CH is required.
Sometimes the microswitch fails to operate altogether, sometimes they work intermittently and sometimes they stay permanently on.
If you or someone you know is competent with a multimeter, the orange wire from the motorised valve is the one that controls the boiler. If CH only is selected to operate then this wire should be live.
Some systems may have 2-Port valves (I think a ZA5 is an actuator for this type of valve) usually there are two valves, one for HW and one for CH. If the microswitch in the CH valve fails the valve will open but the boiler won't start until the HW valve opens and its switch starts the boiler. At this point water will also flow through the already open CH motorised valve and the radiators will heat up too.
If instead you just have one 3-Port diverter valve there is still a microswitch inside that is triggered when the CH is required.
Sometimes the microswitch fails to operate altogether, sometimes they work intermittently and sometimes they stay permanently on.
If you or someone you know is competent with a multimeter, the orange wire from the motorised valve is the one that controls the boiler. If CH only is selected to operate then this wire should be live.
They are usually close to the hot water cylinder as per the example below.
Sorry I got confused earlier and thought it was you that said you had a ZA5 actuator. If you have an old system (40 years plus) you may not have motorised valve/s
Sorry I got confused earlier and thought it was you that said you had a ZA5 actuator. If you have an old system (40 years plus) you may not have motorised valve/s
Two pump system fairly common system on older oil systems.
If installed correctly somewhere you will have relays so heating and hot water can work independently.
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