Have you got a combi boiler which keeps loosing pressure over a period of time? This should never happen on a new central heating installlations but is a common problem on older systems.
Luckily there are only a few things what can cause this problem, so usually it is easy to narrow down the fault but somtimes not that easy to rectify.
Leaking Boiler or Heating Pipework- This is the most common cause of pressure loss on combi boilers. If you have noticed water marks on ceiling, floors or around the radiators this is proberly the cause of pressure loss on your boiler. If you can locate the leaking pipework call a local heating engineer and get them to repair the leak.
You may not always be able to find the leak, but if you can it will save the heating engineer time in turn you save money. If you can't find it you may need to call a specialist to trade the source of the leak.
Leaking Discharge Pipe- Somtimes a part in your boiler called the Pressure Releaae Valve (PRV) fails, if this happens your boiler will also loose pressure although this may be more frequent. You should know if the PRV fails by having a look outside by where your boilers flue is located. If you notice a small pipe outside dripping water you will need to call a local boiler engineer to replace the part.