Updated 23 February 2023

This is a comprehensive continuation of problem resolution of the ESi thermostat which can be found HERE.

Update

Due to the imminent installation of a new boiler with Priority Domestic Hot Water, I will be able to control the water temperature using the unvented cylinders integral thermostat making the ESCTDE/B redundant and therefore I have removed it.

Problem

After the cylinder thermostat was installed, I noticed that the boiler would fire up outside of any scheduled times, checking the programmer settings and wiring, I deduced that the supply to call for heat to the Hot Water Valve was being controlled by the ESCTEDE/B.

I spoke to ESi technical and they confirmed this to be the case when the cylinder thermostat was configured for legionella mode. In this mode, the internal timer of the ESCTEDE/B will call for hot water, (irrespective of the time of day or programmer setting) until the measured water temperature is at or above 60 deg C for 1 hour in order to kill water borne bugs.

As a result of this, I reluctantly disabled the legionella function.

After I received the prompting comment from a blog reader, I thought I would look at a circuit which would only allow the hot water to call for heat based on the programmers scheduled time setting, however, should the legionella mode timer be internally activated, this would proceed as normal, but only within the programmers scheduled time slots.

The simplified schematic below shows this can be accomplished using an interposing relay as a switch for the motorised valve trigger.

Solution – Method of Operation

When the programmer calls for Hot Water, a switched live is sent to the ESi controller HW -ON -COM terminal and also to a Normally Open terminal of a 230v AC Relay contact, the common of the relay contact is connected to the motorised valve (Brown Wire).

When the ESi receives a switched live to the HW-ON-COM, the ESi LED illuminates and an internal connection is made and a switched live appears on the HWS N/O terminal, this output is now wired directly to the relay coil, rather than the motorised valve.

The result of this modification is that when the HW programmer calls for heat, the relay will energise and supply the motorised valve with a switched live from the programmer, should the ESI enter legionella mode, the relay will energise or remain energised depending on the programmers time setting, however, if the programmer is not calling for heat, the switched supply to the motorised valve will no longer be present and the valve will close turning off the boiler.

The advantage of this arrangement is that the boiler firing is dependent on the programmers scheduled times set by the user, rather than the ESCTEDE/B doing this at random times.

The main thing to note is that the legionella setting from the ESCTEDE/B will not reset unless the water, reaches and maintains, a temperature of 60 degrees for 1 hour, this means that the programmers time window must be greater than 2 hours making the assumption the tanks contents will reach temperature in the first hour and maintain this in the second hour.

Obviously the boilers hot water temperature setting must be greater than 61 degrees for this to work.

Modified ‘S’ Plan Wiring Schematic to include Relay Control

My existing central heating wiring centre was the original one and modified when I fitted the ESi and as you can see it was a little bit ‘busy’ and desperately in need of a tidy up!

Looking around for a replacement wiring centre, I saw that a local Screwfix had one in which uses Wago connections rather than traditional terminal strips, the main benefit of this is the tool less connection of wires and a greater number of connection terminals avoiding doubling up of wires which makes installation messy and fault finding difficult.

The Screwfix part number is 621HV and the product is a Wago L32 Terminal Junction Box.

Even though the L32 had a lot of connections, I still needed additional connections for the earth wires and a cross connect marked as connector ‘A’ in the schematic.

The completed Wago L32 wiring centre is considerably neater than the one it replaced, the schematic terminal connections are faithfully recreated within the L32 to aid fault finding or future modifications if required.

Once this was done I changed the legionella setting to operate every 7 days, the installation guide on how to set this up is HERE.