Usually you should replace spare parts for your boiler every 3-5 years. Maintenance should be done every six months to see if anything needs replacing.
In the combo boiler for the central heating? You need a small piece of hose (or it might have a permanent connection) to fix to the mains from the boiler. Then turn the taps near the boiler for the mains and the boiler. You want the pressure to be about 1.3 bar
http://en.wikipedia.org/wiki/Boiler Should be everything you need to know
Yes you can bleed a combi boiler. You do just the same as with a conventional boiler. However, the pressure will drop in your system, so you simply need to adjust it using the little tap (usually below the boiler) to bring it back again (Usually aronud 1.5)
The relief valve should be at least as large (in BTU/hr capacity) as the input of the boiler. A 3.5 million input boiler would need then a relief valve to handle at a minimum 3.5 million BTU/hr.
A new boiler will cost about $3000 for a standard efficiency model, but for a more efficient boiler it can run up to $8000 plus. It is important to have a contractor size up your system. If you buy a more efficient system the boiler will not need to be the same size as your old boiler unit. Keep in mind that you location and seasonal demand will affect the price as well. If a contractor is super busy they will likely charge more since they have plenty of jobs lined up in the future.
The stay tubes basically hold the boiler together, they are thicker than the ordinary tubes and generally dont need to be replaced as often.
what gas boiler alleviates the need for a cwsc
The springs that let the sodas out often need replacing.
In the combo boiler for the central heating? You need a small piece of hose (or it might have a permanent connection) to fix to the mains from the boiler. Then turn the taps near the boiler for the mains and the boiler. You want the pressure to be about 1.3 bar
In order to determine what size boiler you need, you will need to have a Manual J Load Calculation performed on your home.
http://en.wikipedia.org/wiki/Boiler Should be everything you need to know
In order to prevent boiler from rusting (oxidation of magnetite layer) we must have to preserve the boiler with reducing chemicals like hydrazine hydrate.
Auto Electrical Spares specializes in vintage and classic cars. They are one of the very few places you can buy the parts you need for repairing the vehicles.
If they leak, they need replacing. No, if they leak they don't need replacing. If they have been scored or eaten they need replacing. If they only leak they need to be re-packed.
Brake pads have audible wear tabs that make a screeching noise when the pads need replacing, some luxury cars(all bmws) have sensors that let you know when they need replacing.
no it doesnt, it has a timing chain. i doesnt need replacing as often as belt.
There is no set mileage. It depends on many factors. How you drive, where you drive, and the speed at which you drive. I have seen them last 100,000 miles and I have seem some that need replacing at 20,000 miles. There is a warning device that will alert you to when they need replacing. When you hear a high pitched squeal, they need replacing. Another sign is when your master cylinder gets low of brake fluid.