This blog gives Grant a good review and says they’re comparatively priced;
‘For over 40 years Grant specialised in oil fired boilers for off-grid homes, but today the company is leading the charge in the pursuit of renewable heating alternatives. Included in the range is the Aerona³, a highly efficient MCS approved air to water heat pump which delivers exceptional performance, reliability and value.’
Other reviews don’t mention Grant, which is why it’s not on the list. Do continue to let us know how you get along with them.