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iv,e got a worcester 24cdi the pressure keeps dropping replaced the heatexchanger and the diverter valve and the pressure valve can any one help me with this problem

Assuming the automatic air vent, if fitted, and the pressure release valve are ok. Assuming the filling loop is disconnected. If the leak is not within the boiler, it must be somewhere else. How quickly does the pressure fall.
Either you have a leak within the pipes to the radiators or one of the rads themselves. Try isolating as much of the circuit as possible and then retest. You may need to fit temporary isolation valves. Do not turn on CH but test cold. Be prepared for water spillage. draw a map of the circuit and plan carefully what you are going to do.

if the pressure is dropping, it could be a few things,

A leak on a radiator valve, pipework, fitting or boiler.
If the pressure rises before dropping, then it's either the plate heat-ex or the expansion vessel.

Check the pressure when the heating is on, if it rises more that 0.5 - 1.0 bar then it's probably the expansion vessel at fault. If it doesn't rise and the pressure relief valves isn't passing, then it's a leak somewhere.

Why did you change the diverter ?

and what heat-exchanger did you change ?

yes it is a vented system .the pressure drops when the heating has been on and it drops quite quickly .i keep having to refill the boiler every time .I changed the diverter because i thought it was that was causing the drop in pressure

the heat exchanger i changed was the water to water

it is a unvented system.

It could have been the water to water heat-ex, but if there was no signs of leaks on the diverter then there's no way it could have been that.

It seems to be the expansion vessel, you could try re-pressurising but it's quite awkward on the 24 cdi as you have to remove the bypass pipe and the pins are very awkward to get back in.

If I was you I would fit a external expansion vessel.

could be leaking pipe work,expansion vessel reaching 3 bar and over,then dropping pressure thru the prv,if so repressure or relace.there was no need to change the d valve.

could you tell me how to repessurize the expansion vessel and what do i do

could you please tell me how i go about repressurizing the expansion vessel and what i have to do exactly

[quote="htg engineer"]it is a unvented system.

It could have been the water to water heat-ex, but if there was no signs of leaks on the diverter then there's no way it could have been that.

It seems to be the expansion vessel, you could try re-pressurising but it's quite awkward on the 24 cdi as you have to remove the bypass pipe and the pins are very awkward to get back in.

If I was you I would fit a external expansion vessel.[/quote]

could you tell me how to go about repressuring the expansion vessel

Drain central heating system, if you remove the front cover of boiler you will see a big red drum ? this is the expansion vessel.

There's a car tyre type valve on the bottom left hand side, As you will see there's a bypass pipe too close to even get the dust cap off. This pipe needs to come out.

So take out the pipe coming from the bottom of the pump, 2 nuts with fibre washers.

There's 2 spring clips that you need to prise out, and remove the copper pipe (bypass pipe) be careful not to lose the rubber 'O' rings, ensure 'O' rings are in place when replacing.

You can re-pressurise it with a foot pump, to about 0.5 -1.0 bar.

yes i have seen the valve you said about and its facing me a can get at it
with out the pipe there do i still have to take the pipe off

[quote="trev420"][quote="htg engineer"]it is a unvented system.

It could have been the water to water heat-ex, but if there was no signs of leaks on the diverter then there's no way it could have been that.

It seems to be the expansion vessel, you could try re-pressurising but it's quite awkward on the 24 cdi as you have to remove the bypass pipe and the pins are very awkward to get back in.

If I was you I would fit a external expansion vessel.[/quote]

could you tell me how to go about repressuring the expansion vessel

have i got to take off the bypass pipe .I can see the valve above the bypass pipe and have i still got to take off the pipe off the bottom of the pump

[quote="htg engineer"]Drain central heating system, if you remove the front cover of boiler you will see a big red drum ? this is the expansion vessel.

There's a car tyre type valve on the bottom left hand side, As you will see there's a bypass pipe too close to even get the dust cap off. This pipe needs to come out.

So take out the pipe coming from the bottom of the pump, 2 nuts with fibre washers.

There's 2 spring clips that you need to prise out, and remove the copper pipe (bypass pipe) be careful not to lose the rubber 'O' rings, ensure 'O' rings are in place when replacing.

You can re-pressurise it with a foot pump, to about 0.5 -1.0 bar.[/quote]

thanks for help repessured my expansion vessel and the pressure is holding great once again thanks