If this a question you find yourself asking, the following advice may help you identify the trouble. However, this site would advise you not to attempt a repair yourself unless you have the required competencies and qualifications.
If you have boiler cover, it is best to contact your insurance company to send a qualified boiler cover engineer to you. In the UK now, it is actually against the law for unregistered people to work on gas appliances, flues, and fittings, even if they own the defective property.
Little water flow
If the boiler appears to switch on and off, it could be closed valves, air caught in the system, or a pump that’s stopped pumping. The boiler is turning itself off because of in-built safety mechanisms – if it did not, then it could run to dangerously high temperatures.
If there is air in the overall system, then bleeding your radiators could help. Are your radiators warm at the top and bottom as they should be or just partially, at the bottom? If some of them seem cold, bleed them with a special key. If there is enough air to cause your boiler to switch itself off, it should be obvious when you start bleeding your radiators, as air will begin to pour out from them.
A shut valve can inhibit proper water flow as it should. Check the valves on the bottom /base of the appliance – it may have been accidentally closed. If the valve is inside the boiler, it will be unable to be fixed unless you are trained and registered to take it on. In unqualified hands, repair of a broken boiler pump is not possible and a trusted local technician is required.
Low water pressure
If your boiler is leaking in addition to shutting on and off, or maybe there is a leak elsewhere in the house, re-pressurisation of the boiler will be needed. However, if this isn’t the case (no leak) the problem may lie with a defective pressure relief valve and will need a trusted local technician will be required.
If your thermostat has stopped working, the boiler cannot detect the temperature of the water. From this, automatic shut-off will take place to prevent overheating. The appliance may have made the assumption it has already reached the desired temperature. Replacement of the thermostat is necessary. A newer thermostat may reduce your bills and consumption too.
It may also be the case that the heat exchanger may have broken. Replacement is imperative, as it may be dangerous especially if the boiler keeps turning on and off.
In addition, it could be:
- The air in the system: Try bleeding all the radiators. You will know if there was a lot of air in the system because you will feel the radiators exhaust them out. A one-second bleed of air does not indicate a problem.
- If the heat exchanger is broken, it will need to be replaced asap.
- A faulty pump: Get an expert opinion, make sure that your pump is working okay.