Pressure still high

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Hi , i have a grant combi mk11 oil fired boiler that started to get high pressures .This has happened before so i changed the expansion vessel .I checked the pressure in the vessel before i installed it and it was fine a 1 bar ,drained the system and then fitted the new vessel .It was ok for a few hours but has now gone back up to 3 bar :eek:

Has anyone got any ideas what the cause could be ?
 
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Don't know the Grants, but check the fill loop is not passing and also the communication tube connecting to the EV is not blocked. The plate heat exchanger can leak internally and mains pressure can pass to the primary circuit. All these are a possible cause and need to be eliminated. The fill loop is the easiest to check.
 
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Yep as the above says , disconnet filling loop and see if any water is leaking from the valve into the boiler.

Second if the above done show any water then turn off the supply cold water to the boiler.

Run the boiler and see what happens

We are waiting to help you lol
 
Sorry guys bloody internet been down all day yesterday :rolleyes:

I have already disconnected the filling loop so it can't be that

How do i check the other components ? and you say run with the water off ,so i turn the boiler off drain it back down to 1 bar and then run the ch for how long ? i assume there must be another way the water is getting in to the system so what am i looking out for ?

I do value your help gents ;)
 
Increase in pressure is related to either high pressure mains getting into system water. (filling loop or hot water heat exchanger) or expansion vessel related (low volume of air for compression or connecting pipe blocked).
The above have already been stated and there isn't any other way.
Have you checked the schrader air valve on the vessel, if that leaks air, then the air pressure will drop, allowing water to take up more room in the vessel.
If it rises overnight with filling loop removed and heating off then that just leaves the heat exchanger.
As K13 suggests stop the cold water entering boiler overnight, which will prove if the heat exchanger is the cause
 
Right i have checked the valve and its ok ,checked the pipe leading to the vessel and that is ok so i ran the heating with the mains turned off and the pressure didn't move .I now have the heating on with the mains on and after 45 mins the gauge is creeping up .

So i guess this is pointing to the heat exchanger ?
 
Right i have checked the valve and its ok ,checked the pipe leading to the vessel and that is ok so i ran the heating with the mains turned off and the pressure didn't move .I now have the heating on with the mains on and after 45 mins the gauge is creeping up .

So i guess this is pointing to the heat exchanger ?

You guess correctly
 
Remember its the DHW plate heat exchanger you need to replace and not the primary heat exchanger
 
That will be the one on the front of the boiler won't it ? It went up to 3 bar again overnight ,tonight just to make sure i will drain it down to 1.2 bar and then turn the water off and see if it goes up .
 
Just looked at an exploded diagram of the boiler and the heat exchanger is the one i thought it was
 

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