Potterton ep2000 programmer with a potterton roomstat

[daveblue]

I have a potterton ep2000 programmer with a potterton roomstat.

In the mornings I get Hot water and Central heating but in the evenings I get hot water and warm heating.
It would appear that as long as the hot water is set to on, whenever the tank thermostat is green the pump runs.
If the Central heating is programmed as being on at the same time, it works as long as the hot water is also being heated.
Once the hot water is at temperature the Central heating signal from the room stat does not appear to be good enough to keep the central heating going once the hot water has reached temperature.
If I move the Room Stat off then on a few times, I can hear a clicking noise from either the diverter valve or the pump after 4 or 5 attempts I can sometimes get the pump to start up but not always.
It will then continue to run until the room temperature is met.
Once the room temp is met and then the room cools the pump will not come back on unless I switch the room stat on and off a few times.
In this not working state if ever I move the hot water tank thermostat to a higher temp the pump comes on straight away. (So I don’t think it’s the pump that is at fault)
My immediate reaction is that it’s the room stat is not switching the on signal to the pump at the correct level.
I bought a Drayton 24601bq 3 wire room thermostat from B&Q but still have the same issue.

Are there any tests I can do to isolate where the issue is?
What would you look to replace next?

Any help would be greatly appreciated
Dave

 

[D_Hailsham]

Probably the diverter valve is sticking, so one of the micro-switches is not making contact.

How a mid-position valve works explains how to test the valve.

 

[daveblue]

D_Hailsham

Looks like you were spot on about it being the Diverter valve sticking.

The situation I have now is as follows.
When the Central heating is requesting to be on but the pump is not running.
I have found that by tapping the diverter valve header casing a few times I eventually can feet the vibrations of the drive moving the valve.
After a couple of seconds I hear a slight click as it reaches its final position and the pump starts.

Is there anything that I can do to free up the vave or does this situation typically call for a replacement valve?

Dave

 

[D_Hailsham]

Have you carried out the tests given in the link, in particular those for a sticking valve?

Most modern valves can split in two, so the actuator (metal box part) can be separated from the brass body. But you can't do that to older Honeywell valves - those without a small bump on the top cover.

If you can separate the two parts, lubricate the valve spindle with a small amount of silicon lubricant, not WD40 which can rot the 'O' ring seals.

If that has no effect, you will need either a new actuator or a complete new valve (drain down, unfortunately).