Replacing Central Heating Controller – Advice needed.

I think our central heating controller may have gone kaput this evening. It would seem that the ot water override button no longer works.

The system is quite aged it it works and serves us well. ****touches wood****

Looking at the likes of screwfix it wold seem that for sub £50 a better version of what we have could be bought.

Now ….. Are these things DIY or should I call in a local chappie?

System is fairly basic. Boiler, hot water tank, two motorised valves and the pump.

Help.

What clock is it? It’s probably on a universal back plate.

When you say that the over ride button doesn’t work, is that because the light doesn’t come on, or is the water not heating?

Couldn’t turn the hot water off by over riding it.

Digital clock.

Would estimate the control to be fairly old – wouldn’t bt on a universal back plate!

Is the light on the clock going out when you press over ride?

Would estimate the control to be fairly old – wouldn’t bt on a universal back plate!

You’d be surprised. I reckon Theres 25 year old clocks on a universal back plate. If its 6″ x 3″ ish, oblong, then it more than likely is

There isn’t a light but an icon that shows if the over ride has been successful coming on/oing off.

It’s approximately the size you mention.

Hmm.

How would be best to check interoperability?

Before you read all this, BG tiered pricing may be cheaper than the price you’ll pay for a clock, with the added bonus if a pro actually getting it right. If you buy a clock and it’s still not working you’ve lost out.

if you don’t know anything about electrics, then you need to get a pro in.

The reason I ask about a light/icon is that it sounds like a s plan.

An s plan motor head has a micro switch in that has a permanent live, the micro switch is supposed to make when the call for heat opens the valve, but if the micro switch sticks, then the valve will send power down the orange and fire the boiler regardless of there being a call for heat.

The backplate will look like this

If it is, then it’s usually a straight swap, but the wiring diagrams on the back of the clocks will tell you. There will be either jumpers or dip switches on the back of the clock. They allow you to set it to gravity, where the he can be ran on its own, or ch with he, or pumped, where the ch and hw can be ran independently, the clock may also give you the option of setting separate timings for hw and ch.

Okay things are starting to make sense ……

I have a Potterton EP2000 in a rather fetching brown.

It would seem that an EP2002 in iPod white is a direct replacement and could be used on he same backplate.

I guess it’s good practice to change the backplate too but the front plate might be enough

but if the micro switch sticks, then the valve will send power down the orange and fire the boiler regardless of there being a call for heat.

do you mean that?

I thought the valve control was separate to the “call for heat” control.

So if the valve switch (or motor) “sticks”, then the call for heat still happens, but the valve doesnt open…

*newbie hat on*

The valve won’t open unless there is a call for heat from the controls. On an s plan, clock calls for heat, power to stat( room or cylinder) if stat is calling for heat, power to zone valve, zone valve opens, makes switch, fires boiler.

If the micro switch fails, then even with no call for heat, and the valve closed, the boiler can still fire as the valve uses a permanent live no one side of the micro switch rather than a switched live from the controls.

A y plan works by using a 3 port mid position valve, in rest you will get hw heat if the clock and cylinder stat are calling for heat, if you turn the ch on and the room stat has a demand, then there will be 240 on the white which moves the valve into mid position and puts 240 out of the orange, once the cylinder stat is satisfied, this will put 240 onto the grey, moving the mid position valve over to ch only and fire the boiler using 240 on the orange.

EP2000

An ep2000 is a wiring centre also, and would need a proper replacement or to be rewired. It’s done well to get this far! 🙂

If the micro switch fails, then even with no call for heat, and the valve closed, the boiler can still fire

that seems like an odd fail position?

but thanks for the post, get it now.
Haven’t covered all the circuit routes yet in skool, just the component lay outs…

that seems like an odd fail position

They stick in operation, or just short internally. It’s an easy diagnosis, as you just check that theres no f
Supply to the synchrons then pull the oranges out and see which has 240 on it.

The Honeywell iPhone app has some good diagrams on it.

Paul I don’t follow.

This listing for a EP2002 suggests its a straight replacement for the EP2000 allowing the same (in situe) wiring to be used.

http://www.heatingcontrolsonline.co.uk/potterton-myson-ep2002-programmer-p-118.html

Perhaps I am being dim 😳

Sorry, an EP2002 should go straight on, it’s the same backplate as a 2000 from memory, with the same wiring too. You would need to do a bit if re-wiring if you were going to fit something else instead.

cheers paul.

Soooooo

If I bought an EP2002 and swapped in the new backplate with the same wiring layout as the current backplate all should be okay?

I understand I could just just my current back plate and the new fascia bit but some sources seem to indicate this isn’t best practice.

Thank you Paul 8)

The whole reason to buy one worth the same backplate is so you just remove one and refit another. No need to change the backplate.

But again, if your not competent, get a pro in.

do the controllers fry often?

EDIT, Oh and Paul, do you agree with this diagnosis?
http://singletrackworld.com/forum/topic/plumbing-problem-possible-hot-water-leak#post-3951535

The obvious thing to do is tie the ballcock up and have a cup of tea. If there’s any sort of leak, the level in the tank will drop. That’ll tell you if you have a leak. But if there are a load of old dead legs in the system, then both theory’s are viable, if for example there is a large head of water with a small leak at the bottom, then it could easily be a leak.

Think of it in simple terms of a vertical run from tank in loft to under the floor downstairs. The pipe under the floor has a small leak. If the downstairs tap has a very short run off the vertical leg, whereas the upstairs one goes round the upstairs, then the upstairs one will have a larger volume of cold water to run through before the heat gets there.