Hi, I am hoping someone may be able to throw some light into what might be causing the problem with our central heating system. I have a two zone central heating system (house plus annex). We have two heating thermostats, one in each zone, two Drayton ZA5 actuation valves, a Megaflow system and Potterton boiler. The heating and hot water come on twice a day in both areas. However the annex heating is required more as it is for an elderly relative and we have noticed that when the annex is on and our house is off at the timer, the central heating is getting to our radiators and they are hot. I can turn the hall thermostat off but they still get hot. The only way to stop them getting hot is to turn each one off by its thermostatic valve. Any advice please?
Radiators getting hot when off in two zone system
- Thread starter Lenihan
- Start date
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Hi, Some questions and a couple of tests for you.
1. Has the system ever worked properly?
2. You say you have two Drayton ZA5's is this just for the heating control? If so, what is controlling the heating of the Megaflow cylinder?
3. Can you confirm that the Drayton valves are both two port valves please?
4. Does the fault occur the other way around or not? [By this I mean, does the annex heating stay in operation when the heating there is turned off, but the main house heating is still on. To test it, start with both systems 'on' at their programmer and thermostat, then switch only the annex off, do the annex radiators stay on? This may help determine if the wiring is incorrect and that the two systems are wrongly interlinked.]
5. Starting with both systems off now fire up the annex only. Does the house heating come on now?
1. Has the system ever worked properly?
2. You say you have two Drayton ZA5's is this just for the heating control? If so, what is controlling the heating of the Megaflow cylinder?
3. Can you confirm that the Drayton valves are both two port valves please?
4. Does the fault occur the other way around or not? [By this I mean, does the annex heating stay in operation when the heating there is turned off, but the main house heating is still on. To test it, start with both systems 'on' at their programmer and thermostat, then switch only the annex off, do the annex radiators stay on? This may help determine if the wiring is incorrect and that the two systems are wrongly interlinked.]
5. Starting with both systems off now fire up the annex only. Does the house heating come on now?
Hi Stem, thanks for reply. The system was new in 2009 and has always worked fine. I believe the ZA5's are 2 port and for heating only and there is a Honeywell Motorized valve for hot water. Test done and it appears to be working as it should. I gave the two valves a vacuum and a gentle tap, as read that the valve can get stuck and amazingly it seems to be working fine! Not sure if it is fixed or the fault maybe intermittent. However I will come back here if it continues. Watch this space! 
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