High Pressure issue (Mega flow - Worcester 24i)

Discussion in 'Plumbers' Talk' started by andy2605, Jan 17, 2020.

  1. andy2605

    andy2605 New Member

    Hi, i recently had an issue with losing pressure on my boiler. A plumber came round and carried out a power flush and replaced a PRV, he also added a Magna clean filter and checked the expansion vessel which he said was OK.

    This sorted the issue for about a month. I now have the opposite problem. When the system is off the pressure is very stable, it is also fine when the hot water timer kicks in for an hour or so in the morning. However when the heating comes on the pressure rises well into the red zone. (Regardless of whether the hot water is on or not)

    The plumber came round and checked the expansion vessel and said it had pulled more pressure (which i thought was strange) and corrected it to 0.75 i believe?

    The same issue is still there regarding the pressure raising when the heating is on.

    Any advice would be great.
  2. terrymac

    terrymac Screwfix Select

    If pressure is getting to ,or close to 3 bar when central heating is on ,and when system is cold pressure was/ is 1 bar ,then the EV is not functioning as it should ,or it is undersize for the systems volume of water.

    If pressure rises when boiler is inactive for sometime ,that's a different issue.
  3. andy2605

    andy2605 New Member

    Hi, yes it is only an issue when the heating is on. According to the plumber the ev is pulling pressure from somewhere as opposed to losing pressure but said it appeared to be ok? He also suggested the heater exchange may be an issue but said there were no obvious signs I.e leaking.
  4. andy2605

    andy2605 New Member

    Does the EV play a part when the hot water only is on? I only ask as the pressure is fine when the hot water is on (without the heating)
  5. Mike83

    Mike83 Screwfix Select

    The vessel does play a part when HW only is on but usually a smaller part.
    The less water that is heated the less expansion there is.
    The HW circuit is usually a lot smaller than the heating circuit.
    How many radiators do you have?
  6. Mike83

    Mike83 Screwfix Select

    It sounds like the plumbed may not be checking the vessel correctly.
    The vessel can’t pull in pressure. It can lose pressure though.
    It may seem like the vessel is increasing in pressure if he tests it whilst the heating system/boiler has water in it.
    The Teach likes this.
  7. TheMorg

    TheMorg Active Member

    Could be the flexi hose to the expansion vessel is blocked - lets enough in over time to make the vessel appear charged even with the boiler depressurized, but doesn't actually allow for expansion.
    Mike83 and The Teach like this.
  8. The Teach

    The Teach Screwfix Select

    andy2605,you really need an operative experienced with all heating systems including mains water items who can service expansion vessels and leave a written report. They seem to be quiet rare these days :p

    FGA :confused:
    Mike83 likes this.
  9. andy2605

    andy2605 New Member

    Thanks for all the comments. I have decided to get a second opinion from another plumber that’s been recommended.

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