Normally there will be a stopcock on the mains water supply as soon as it enters the property. This would be under the kitchen sink in a lot of cases. Once located turn clockwise until it stops. Then open the cold tap. Water should stop after 5 to 10 seconds. If it does you know that has isolated the mains water supply. Close cold tap again. If there are tanks in the roof space the large one could be drained by opening the shower or bath hot and cold taps. Once stop running remember to close. The heating cold be drained at the drain valve at the boiler.
Have a cloth under air vent at radiator. Open air vent with air vent key anti-clockwise. If air comes out keep open until water starts to come out. Then close. Take care not to remove vent to far. Only opening ½ to ¾ turn should be enough.
It is recommended that only competent Gas Safe engineers work on gas boilers. Contact Gas Safe registrar website for your nearest local qualified engineer.
The flushing syphon is showing signs of wear. Remove cistern lid. Be careful doing this as some lids require button to be screwed out first. Gently lift lid and this will indicate if button is screwed in. If it is turn anti-clockwise. The syphon will normally be attached to a base that is then attached to the toilet cistern. The syphon should remove from base with a slight anti-clockwise turn. To completely remove you may have to detach from the push button, but this should be visible. Take to your nearest plumbers’ merchant. Hopefully they will have a direct replacement, that will not require the base to be removed. Once replacement obtained, install in opposite sequence as removal.
The Megaflow is an unvented hot water cylinder, where the water to it is supplied directly off the mains water supply, i.e. no cold water storage tanks. There should a label on it to indicate that it has been properly installed. There should also be a commissioning booklet that was completed when installed and service history. The installation and servicing of this type of cylinder requires the person to have the professional accreditation of G3 Building Regulations of Hot Water Systems & Safety certificate in the UK. Treat the Megaflow as your oil or gas boiler and have serviced annually for best operation and safety.
Do not touch any electrical devices or switches. Turn off water as described in question 1 to limit damage. To progress further to locate problem we would recommend that you are a very competent DIY’er, or contact a plumbing and heating engineer.
There are a number of options. If a screw down type, there is a washer inside that can be replaced. If a quarter turn type, you can get you new centre pieces. Or replace tap. With replacing any of these parts it sometimes does not completely cure issue, as other parts are maybe also worn. Sometimes the best and long term action is complete new replacement.
One of the best and most effective methods of unblocking a toilet is using a mop as a plunger. This causes a vacuum that after number of plunges can remove blockages in a large number of occasions. If this does not resolve, look for roding eye, sewer cover outside dwelling. These are locations where it can be removed to allow a sewer unblocking rod to be used to try and clear blockage. If mop does not resolve and do not have equipment or knowledge to continue, contact your local drain unblocking company.
Sounds like sludge in radiator. To cure this the radiator or heating system will require flushing. Local merchants supply flushing chemicals. This needs installed into heating system. To do this some water needs drained off and the chemical installed into heating system to get circulating around complete system. The chemical cleaner should say on it what size of system it will supply and how long to keep into system. I would recommend flushing, filling and flushing again. To also help you can remove each radiator and flush out, buy turning upside down and fitting a garden hose at one end and letting run completely through to other end until water runs clear. You want to make sure and get all chemical out of system, as if not can be aggressive to pipework, fittings, radiators, etc and cause leaks. If this does not cure, would recommend getting an engineer to power flush.