Worcester Bosch 28CDi RSF Pressure Problem

31 Oct 2007
Reaction score
United Kingdom
I have a Worcester Bosch 28CDi RSF boiler which is about 8 years old. The pressure on the gauge drops to zero about 4-5 hours after running the central heating. I have had this problem for about 18 months and has been getting progressively worse. Initially refilling every few weeks but now daily. This problem is not coverred by the installation and fault finding mauals or any of the installers or user materials from the Worcester Bosch Web site.

My initiall thoughts were obviously a water leak! So far have pressurised the boiler as high as mains pressure would allow and inspected all over the boiler for leaks with boiler off and cold and running for hot water and running for heating. Nothing found around the boiler aside from the vent cap on the top left hand side which has watermarks from it, but oberved no significant leak. When not running the presure holds and when using hot water only the pressure holds. Also inspected the piping around the house. No signs of leaks anywhere. Luckily with a full cellar I have access to all fittings apart from the two upstairs bedrooms and there does not appear to be any water leakage marks on the plaster on the rooms below. Or leakage on any of the pipework around the house.

The diverter valve was replaced about 2 years ago and boiler has been regularly serviced as house was rented out. However not had a second opinion on this fault yet.

Could this be internal leakage within the boiler when running? Any ideas.
Sponsored Links
Replace the pressure relief valve as this would appear to be letting by, check outside for the pipe discharging.

You are causing problems for yourself in that you are introducing fresh water into the boiler every time you refill. The scale build up around the heat exchanger etc. will reduce boiler efficiency, maybe causing 'kettling'.
Good idea to look at the PRV pipe. Have traced the pipe run and found it going to the flat bed roof over a utility room. Amazed that I never noticed it there before! Put a beaker under it to collect what ever leaks to confirm this is the fault. So far nothing but pressure has not dropped yet. If i dont get any water i'll put another message up. Thanks for the advice.

As I have been filling the CH circuit often, should I put some treatment in it to get rid of any scale build up then flush it out? Any advice on products I should use and where to get them.

Sponsored Links
Never been sure about the effectiveness of chemical descalers insitu. Will leave that to others. It would have been good to have had an inhibitor in the system, but yours will have been well diluted by now :LOL:

Knowing where the leak is coming from may have been resolved, but make sure the underlying fault of why the PRV is blowing is corrected. It may be just muck under the washer sealing seat of the PRV.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local