From the photo in the following link, it looks like it might be a Teplofit HT1503. Whilst it may help with identification, unfortunately you can't buy from this site unless you want 500 units or more. http://www.alibaba.com/product-detail/Chrome-TRV-thermostat-head_1576678230.html Solar probably bought a large quantity badged for them.
You could always take it along to a good plumbers merchant, they may have a replacement that may fit, or an adaptor that will allow another head to be used.
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