Loss of pressure in boiler, no obvious leaks, water pressure switch changed plus pressure release valve

Sounds like the water inlet valve to your hot water heater has been closed (turned off) If the tank has no water coming in, it can't put anything out.

I assume losing pressure through the PR means Pressure Relief Valve (PRV) or temperature pressure (TPR). Open in TPR may mean boiler is overheating/overpressurized. Open in PRV means the Pressure Reducer/Fill Valve in the fill line of the boiler is broken.
House Water Pressure in a home is 30/40 PSI min to 60-80+PSI max.
Boiler PRV/TPR are set at 30 PSI open (SYSTEM PRESSURE) so too high a house water pressure will open the PRV/TPR. Replace the reduction regulator on/in the fill valve assembly

if you all ready replaced is not suppose to leak more water this pressure release valve are reated to 75 psi pressure some of them

Hi,
The pressure built up in the boiler and the relief (safety) valve released some water to relieve the pressure...
Either the exspansion tank is bad or the fill valve is leaking by...
This causes excess pressure to build in the boiler...

heatman101

refere to manual check for override switch loss of pressure no problem re-pressurise and check for leak top of rad valve good place to start

http://www.worcesterbosch.com/Go there see if you can get some help.

The movement of the diverter valve is critical on this appliance, and is located on rear right of the boiler, when hot water is turned on, theres are two microswitches, which must break (they both close in Central heating mode), if pump is running, it is recognising the hot water demand, check microswitches are breaking, if not, it tends to be a defective servo valve (located above the water valve), or a blocked/ restricted control line (small copper tubes which connect into the servo valve)

So the boiler relief valve is leaking? What is the boiler pressure when the relief valve leaks? The relief valve will have a pressure rating on it. If the relief valve leaks when the pressure in the boiler is lower than the relief valve setting then its just a bad relief valve. If the relief valve is leaking when the boiler pressure gets above the relief valve pressure setting then the relief valve is doing its job and there is another problem. Several things can cause the boilers pressure to go higher than the relief valves setting. It could be a bad expansion tank or one that needs to be drained and re-charged. It could be a bad cold water fill valve that isn't shutting off and is over filling the system, rasing the pressure above the relief valve setting. If this boiler also does your domestic hot water, I have seen where the domestic hot waters heat exchanger has a hole in it and the domestic hot water is mixing with the boilers water and over pressuring the boiler.

generally preesure problems are caused by the following- obviously a leak, bleeding of rads without topping up the pressure, pressure relief valve passing( probably an integral part to the boiler), or potentially a problem with the expansion vesell.
the expansion vessel is a tank which
holds water and air- it should be pressurised with air by about 10 psi or up to 1bar, if the diaphragm has split this ill cause pressure problems all day long

hope this info helps