Urgent Help Required Boiler Fitter

The gas engineer returned this morning around 10pm with an electrician, as requested to sort out electrical problems. Apparently the gas engineer failed to connect wiring correctly, the problem was quickly sorted out. I was not present at the time due to a very important appointment. When I returned around 1pm, engineer said everything was working perfectly. We paid for the work, I paid half in cash, OH agreed to pay the remainder via credit card. but engineers card machine was faulty, so we agreed to pay by cheque as the was no other alternative. We obtained certificates, receipts and boiler manuals. About one hour later I thought I would try to use the new boiler to obtain hot water to complete some cleaning jobs, I switched the boiler onto the hot the water facility only, waited about 1 hour. Turned taps on, no hot water all.
I advised OH to cancel the cheque to the engineer with the bank immediately, at the cost of £10.00. I contacted the gas engineer again and reported that we did not have any hot water supply and was cancelling the cheque due the to these reasons.
His reply was that the boiler was had been fitted and was in perfect working order. During my phone call, he admitted that he did not test the hot water facility of the boiler, plus he thought that there maybe an air blockage in the system. He said he would return next Thursday after 5pm with the equipment to resolve the air blockage. I have emailed him concerning the reasons as to why he failed to complete the necessary tests.
I have great respect for any genuine tradesmen and will always offer a tip for good service.
Legally, if I refuse to pay him, I have broken the contract and he can reclaim everything via a court order, plus costs.
We are both pensioners and don't have enough money to fight a court case.

Please do not respond to this thread unless you can offer genuine advise. I really do no not need any abuse at all, as I have not done anything wrong but just asked for advise. I don't need unqualified people arguing amongst themselves. I welcome any advise from anyone who is very qualified in heating & plumbing or anyone regarding the law on consumer law concerning heating and plumbing engineering.

Many thanks

Hi to anyone is interested. Here is the reply from the s engineer that I received yesterday.

It would appear to be an airlock in the system, this is usually the case when the pump is replaced, when we installed the boiler the demand for hot water was working properly and everything was fully sufficient for full commissioning. You requested us to change the boiler and diverter value which has been fully completed, not to diagnose another other problems on your system.

I will again come back on Thursday to install an automatic air vent which hopefully solve your problem.

As we have completed the job we quoted for, payment for the completion of work will be required on Thursday and I am afraid we will no longer be accepting cheques for payment.

Firstly, if he was aware that there may be a possibly of an airlock in system, which affected the pump after the new boiler was fitted, why didn't he sort it out. Secondly the demand for water had not been working and never has been. Quite clearly everything was not working properly. Not sure what an automatic air vent will do.
I thought its was the engineers responsibility to fit the new boiler and ensure that it was if full working order, providing heating and hot water. I have not asked him to diagnose any new problems, just fix the ones he has caused. As for paying by credit card, no problem with that, if his card machine is working.
I have contacted Gas Safe, they will be completing an inspection within the few weeks. I have no desire for compensation or to make anyone's life a misery.

Many thanks to all