No DHW / pump not running - 'A' Rated pump fitted

This article relates to Xcel / SSCYL / DS-xxx-xx thermal stores supplied during early to mid 2013, fitted with plate heat exchanger DHW assemblies using 'A' rated pumps.

It has been reported in some instances that thermal stores shipped between April 2013 and August 2013 have exhibited intermittent or complete failure to deliver domestic hot wahter when demanded. If the heat exchanger pump on the affected stores is observed when DHW is demanded, the LED on the pump usually shows green briefly, then turns to flashing green/red or solid red, and the pump fails to operate.

As of April 2014, all thermal stores were fitted with new 'A' rated Wilo pumps (Yonos Para RS 25-6). The characteristics of these pumps mean that their running currents are much lower than previous models. The effect of this is that the lower current being drawn throughthe flow switch (that energises the pump when DHW is demanded) can prevent the flow switch from 'latching' into full conduction. The resulting low output voltage to the pump causes the pump to register a fault and stop running.

From August 2013, a relay has been fitted at the factory between the flow switch & pump to eliminate this problem. For units currently in the field shipped prior to this ammendment, a pre-wired relay can be supplied free of charge by Specflue. An installation guide / wiring diagram for this is attached below.

Attachments:
Xcel-DHW-pump-with-relay-wiring-instal-instructions-SPDT-relay.pdf