Turn on the voltmeter and attach a probe to different terminals on each component for a reading. What you do with the results is up to you if you are a heater tech. If you do not know how to use a voltmeter - you are already in trouble.
You need to determine the: gas heater size for the specific pool/spa (with spa use no less than 400,000 BTU). ( how fast do you want the spa to heat to temp?) length of the gas run from the gas meter to the heater pad. size of the gas meter size of the gas pipe at a minimum. Ken
a heater/ spa store
The starting price at Leslie's Pool Supply for a spa heater is $197. The most expensive spa heater is $264. Shipping varies based on the price of the order.
If a spa heater has stopped working or a new one is needed, Amazon has a big variety of heaters. The prices range from about $200 to $10,000 not including shipping.
Most people would want the spa hotter, so in that case there is no way to use only one heater.
no you need a stronger heater specifically designed for a swimming pool
There should be valves to redirect the water to and from the spa. Ken
yes the nominal voltage in the UK is 230v but can fluctuate between 220v and 250v so yes
You should check reviews and compare prices. You can do both at www.nextag.com/hot-tub-heater/compare-html
I would go with no less than a 250,000btu. Reason being is the smaller you get the more time it takes to heat the spa thus using more gas. I prefer a 330,000btu. It will heat the spa in 50f water to 100f in approximately 30-40mins.
That depends on where you are and the quality and extent of the work.
No