Temperature pressure relief valve dripping

Our megaflo Worcester Bosch (Greenstar CDi Classic) switched itself off earlier today and then there were problems when I tried to restart it.  It kept flashing two T's on their side, ie -I I- alternately with a reducing figure which I assume is a temperature.

Since then, there is a slow steady drip visible through a small 'cage' (see photo) which sits within a length of copper pipe.  The copper pipe feeds directly into the side of the Temperature & Pressure Relief valve (a large round metal thing which is attached to the front of the water store - a Stelflow unvented hot water storage cylinder).

There is also a further steady drip from the bottom of a copper pipe which comes from the bottom of a small white tank (expansion?) located above the water store.

I'm trying to get hold of our plumber but in the meantime I'm a bit worried.  I'm guessing that both of these things are doing what they should do in the event of problems, but do I need to switch off the heating or water?

Many thanks


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  • jefaz07
    jefaz07 Posts: 530
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    edited 23 November 2023 at 9:02PM
    Is the dripping water hot or cold?
    The ‘cage’ is called a tundish. The 2 T’s are what a Worcester will do when it is powered up. 
  • Lulu58
    Lulu58 Posts: 307
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    jefaz07 said:
    Is the dripping water hot or cold?
    The ‘cage’ is called a tundish. The 2 T’s are what a Worcester will do when it is powered up. 
    Thank you for getting in touch jefaz07, and for the information regarding the tundish and two T's.

    The drip through the tundish is cold and is dripping faster than it was.  I had a shower earlier to try and remove some of the hot water as it was dripping really fast.

    The drip from the pipe connected to the expansion tank is also cold.
  • markin
    markin Posts: 3,720
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    Expansion tank may have failed, so its over pressured when heated, Over pressure valves often need replacing as they tend not to reseal after opening and getting dirt in them.
  • jefaz07
    jefaz07 Posts: 530
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    Lulu58 said:
    jefaz07 said:
    Is the dripping water hot or cold?
    The ‘cage’ is called a tundish. The 2 T’s are what a Worcester will do when it is powered up. 
    Thank you for getting in touch jefaz07, and for the information regarding the tundish and two T's.

    The drip through the tundish is cold and is dripping faster than it was.  I had a shower earlier to try and remove some of the hot water as it was dripping really fast.

    The drip from the pipe connected to the expansion tank is also cold.
    You need someone with a G3 qualification. Doesn’t sound like a TPRV issue as the water is cold. Have the expansion vessel and reducing set checked. 
  • Lulu58
    Lulu58 Posts: 307
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    edited 24 November 2023 at 7:20AM
    jefaz07 said
    You need someone with a G3 qualification. Doesn’t sound like a TPRV issue as the water is cold. Have the expansion vessel and reducing set checked. 
    Thanks, jefaz07. I've just looked up the G3 qualification. Not sure our plumber has that but will ask. He hasn't come back to me as yet. I'll contact him again.

    There was a noise prior to the boiler switching itself off that sounded like a motor, maybe a pump trying to switch itself on but failing and starting again. It happened about 8 or 9 times, then the boiler switched off. Not sure if that's a red herring?

    If I can't get our plumber round, am I looking for a plumber, heating engineer, boiler engineer, what?

    Also, do I need to turn off the heating or water in the meantime?
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    edited 24 November 2023 at 7:36AM
    Yes, it's doing what it should do, Lulu, so don't worry. But, yes, you should stop heating the megaflo (DHW) until it's sorted.

    You can keep heating your radiators (CH). 

    The device that is allowing the water to escape via that tundish acts on pressure - it'll open to discharge excess due to a fault. The device is not triggered by 'temperatures', expect in the sense that it's the expanding hot water that causes the pressure increase. (Just info, since you seem to have a good idea what's going on :smile: )

    The tundish is there as a visual indicator of something being wrong - so that worked too!

    Yes, the white tank is an Expansion Vessel (EV) which is there to take in expanded water from the Megaflo when it's heated up. Inside is a rubber diaphragm, with the Megaflo water on one side, and compressed air on the other. Expanded water can come and go, and this keeps the pressure steady. If air is lost from the air side, then the EV will always be full of water, so no more can get in when it's heated - pressure increases, and the safety valve opens.

    Your EV will most likely need a recharge or air (if the diaphragm is intact) or replacement (if not).

    The safety valve might also need replacing, as they tend to carry on dripping once activated.

    There shouldn't be a drip from the EV itself, so my suspicion is that the vessel is kaput. Make sure to catch all drips to prevent any damage.

    A bit strange that the boiler seemed to stop working - there's no reason I can think of for this, as it doesn't 'know' there's an issue with the Mega.

    Is the 'system' pressure ok? The boiler, radiators, and heating coil inside the Mega are 'one', and sealed, and the pressure is shown on the boiler display. (And there's a separate EV - red - for this.)
    What is the system pressure, and does it stay pretty constant when hot and cold?

  • If you call megaflow they will come and repair it and they have a scheme where they guarantee to fix it for £250 (this is what I did last year) or of it can't be fixed they refund the £250. I got a free tank out of this as it couldn't be repaired.  It might be worth going that route if you can't find anyone to look at it. 
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    Lulu, could you post a photo of your EV, please? Try and show where the drip is coming from.
    Can you see a Schrader valve on it - a car tyre valve? Is there water seeping from that?

    If it's from the copper pipe joint at the bottom, then it's likely just not done up properly (never was), and the increased pressure has exposed this. Easy for a plumber to fix.

    You can safely remove the valve cap, and briefly press the valve pin - use something blunt. If it 'hisses', then hopefully your EV is still ok, and just needs more air. If nothing at all comes out, then there's no air left at all, but the diaphragm is still intact. But if any water comes out, it's kaput, so a new EV will be needed, which might make the fixed-price repair mentioned by hb143 a good call. However, if the EV is actually ok, and just needs air-charging (just like you'd do on a car!), then it could be costly, as recharging is just 20 minutes of pumpin'.

    If you have a trusted local G3 GasSafe, then that's usually the best first call. Have you had it serviced at all? And, how old is it?
  • Lulu58
    Lulu58 Posts: 307
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    If you call megaflow they will come and repair it and they have a scheme where they guarantee to fix it for £250 (this is what I did last year) or of it can't be fixed they refund the £250. I got a free tank out of this as it couldn't be repaired.  It might be worth going that route if you can't find anyone to look at it. 
    Thanks for your post, housebuyer143. When you say call megaflow, what do you mean, call Stelflow the company name on the cylinder?

    Sounds like you got a reasonably good deal.
  • Lulu58
    Lulu58 Posts: 307
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    Yes, it's doing what it should do, Lulu, so don't worry. But, yes, you should stop heating the megaflo (DHW) until it's sorted.

    There shouldn't be a drip from the EV itself, so my suspicion is that the vessel is kaput. Make sure to catch all drips to prevent any damage.

    A bit strange that the boiler seemed to stop working - there's no reason I can think of for this, as it doesn't 'know' there's an issue with the Mega.

    Is the 'system' pressure ok? The boiler, radiators, and heating coil inside the Mega are 'one', and sealed, and the pressure is shown on the boiler display. (And there's a separate EV - red - for this.)
    What is the system pressure, and does it stay pretty constant when hot and cold?

    Hi ThisIsWeird, and thanks for your post and the information given which is really helpful. I hate it when we get trades people round and I haven't a clue what I'm talking about!

    I'm not sure how to stop heating the megaflo. We have the heating and water on 24/7 via a programmer which is controlled by two thermostats on the ground and first floors. Looking at the programmer, the only way I can see to switch off the water is to change the programme so it doesn't come on at all but I'm not sure if it will allow me to do that.

    I've got a bowl under the EV drop. It filled to about 1/3 overnight.

    I wondered whether the boiler switched off because of the motor/pump type sound I heard (see post above). We've had problems with our motorised valves before.

    The display on the boiler says 62 at the moment and the pressure gauge is where it is normally at around 1ish bar.

    Now is not the time for the plumber to go AWOL!!
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