we had a new eleticaire heater installed can i demand a certificate for the work done?

Hello. Yes, this job is under Minor Works Certificate (bs7671) if your heater is just a replacement or Electrical Installation Certificate (BS7671) if new circuit was introduced. All electrical work must be inspected ,tested and certified by NICEIC or Select registered electrician. Building Act 2015 (Scotland)

This might not be as straight forward as it seems. You should be able to get the electrician to give you a certificate for the heater but if it was a remove and replace (like for like) without any wiring then he would not be required to certify it. However if a new cable was involved then a certificate is required together with the correct RCD protection at the consumer unit. Even if he wasn't required to issue a certificate a good electrician would have tested the circuit and should be able to issue one for you.