DIY Doctor

EP2002 Controller With Potterton boiler and Controlling Heating and Hot Water Separately

Postby boilerapprentice » Tue Oct 02, 2018 8:24 pm

Apologies for the in-depth description but the issue with my central heating is starting to become a nightmare.
Basicially I have a Potterton boiler, EP2002 controller, MPE322 3 way value controller and a thermostat in the room and one on the hot water tank.
The problem is that I would like to control the heating and the hot water separately, ideally controlling the hot water using the timing system and the heating using the room thermostat.
From my understanding the EP2002 allows me to do that (theoretically) but I have the following issue.
If I turn the hot water on via the EP2002 controller switch (central heating switch turned off) the MPE 3 way switch sets itself correctly, the pump starts, and the boiler fires up. No problem so far. If I now turn the Central Heating slider on the EP2002 to the on position (room thermostat turned up) the MPE322 switch does not alter its position, and hence the radiators do not heat up.
If I switch both sliders to the off position and then just slide the Central Heating slider to the on position the MPE322 switch changes its position, the pump starts, and the boiler fires up….resulting in the heating coming on.
However if I now turn slide the Hot Water slider to the on position the MPE322 does not change its position, and hence the radiators continue doing what they should but the water does not heat.
Now it I remove the EP2002 controller and change the setting on the back to lock the sliders and re-install I can switch the central heating slider to the on position (which automatically slides the Hot Water slider to the on position) and the MPE322 switch changes to the mid point, heating both the radiators and the hot water. I can now control the switching of the MPE322 using the thermostats (room and boiler) but can not control it using the EP2002.

I personally think the controller is at fault…but not sure. I would welcome any thoughts on this issue.
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Postby collectors » Thu Oct 04, 2018 11:02 am

It depends on how old the system is? With certain valves & wiring you used to get what they called hot water priority systems, so even if you switch everything on, the system would first heat up the hot water & when the cylinder stat was happy it would switch over to heating the rads. You would need to find out what 3 port valve you have installed to confer this. If this is the case, it would mean getting a new 3 port "Mid position" valve & a bit of jigerling with the wiring.
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Postby boilerapprentice » Thu Oct 04, 2018 6:56 pm

Thanks for the reply. Very much appreciated. The valve is a 3 port value allowing the hot water and central heating to heat at the same time. From further investigation I am convinced this has never been wired correctly. I am going to have a better look at the weekend. Once again thanks for your response.
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