Let the money for Ukraine flow!

Try better tube insulation and also there a big gap in the grill. Try covering it. A bigger copper heating coil should be also in consideration, or make two heating coils. Or ditch out the grill and make a large coil and put wood inside. No pump required for smaller pools.. Probably You would end up whit multiple insulated copper coils. Stacked car radiators should also do the trick like @mholiv said, but You should put the pump on higher speed so they wont start to boil inside. Be sure that the rubber hoses are high temperature proof. Or just put a thick steel barrel into the pool and put wood or coal inside, just make sure to add insulation on bottom so Your pool wont have a burned hole on the bottom.

Hi. What He says about “good condition”? How many years of usage, what type of water was used, how many shots per day. Descaling of the boiler can be expensive and/or very tiresome. Ask about warranty. Check the heat up time before ready. If it’s very long do not buy, the boiler can be in bad shape. If You are really happy whit the setup, You shouldn’t consider a change. Boiler is a boiler, E61 grouphead is a E61 grouphead. You wont feel a big difference in taste, only in the workflow. Going from eg. Barista Express to Mara X is a big jump in everything. But differences between E61 to E61 machines do not play a larger role in the image. There are HX models and Double Boilers, even few Single Boiler models, but in most cases the operation is nearly the same (excluding cooling flushes or waiting for steam to froth milk). I understand upgrading from HX to DB. This can be a good machine, but are You willing to pay money for a used model, just be aware it can be a waste of money. Especially if You are buying for a business. But if You have the technical skills and want to do some tinkering, You might buy a new boiler from ECM and assemble it my Yourself.