Heat Exchanger - for use in Hippo Showers ONLY. 
Please check before ordering this part as its has recently been updated
These can be replaced by our Qualified Gas Person, by sending your boiler unit back to Hippo Showers. Or, if you have your own gas engineer, they are simple enough for them to replace. 
The key is to NOT let your shower freeze... but if they do, this is the part you need.