position of expansion vessel in relation to unvented cylinder

[unrulyg]

hi all, would be grateful if someone can shed some light. i'm based in the UK if that helps.

i know nothing about plumbing or central heating but have been having issues with my boiler and unvented cylinder. a g3 qualified engineer came over today and said the expansion vessel was blocked from being serviced by the ceiling and that the expansion vessel was also in the wrong place. he said it was connected to the hot water rather than the cold supply which he said would explain the excessive dripping in the tundish.

i have other problems with the boiler such as leaking flue etc that he will also fix.

my question is, is he right about the expansion vessel being in the wrong place and that it shouldn't be connected to hot? video here:

 

[unrulyg]

Would really love some opinions on this one please?

 

[Johntheo5]

The position should be lowered to gain access to the schrader valve to enable checking the precharge pressure and the EV outlet should be teed in to the cold water feed, downstream of the expansion refief valve, it will last longer as the diaphragm will not be in contact with very hot water when connected to the hot outlet.

 

[Madrab]

Technically he's wrong on both counts.

Yes, the EV could be lower for servicing of course but nothing a pair of steps wont sort and ideally the EV feed would be taken off the cold supply into the base of the cylinder, so it's not exposed to the warmer temps from the Hot Water side, as suggested.

Is what's been done wrong? No. Just because the EV is on the hot side wont be the cause for water dripping at the tundish, that's normally either the EV's pre-charge pressure/membrane compromised or the Temp & Pressure Relief/ Pressure Relief valve (there are both) passing.

 

[unrulyg]

Technically he's wrong on both counts.

Yes, the EV could be lower for servicing of course but nothing a pair of steps wont sort and ideally the EV feed would be taken off the cold supply into the base of the cylinder, so it's not exposed to the warmer temps from the Hot Water side, as suggested.

Is what's been done wrong? No. Just because the EV is on the hot side wont be the cause for water dripping at the tundish, that's normally either the EV's pre-charge pressure/membrane compromised or the Temp & Pressure Relief/ Pressure Relief valve (there are both) passing.

thanks for this

that's normally either the EV's pre-charge pressure/membrane compromised or the Temp & Pressure Relief/ Pressure Relief valve (there are both) passing.

how are each of these potential problems(compromised membrane and temp/pressure relief valve) diagnosed and resolved? obviously i am not qualified, you're always told to go and seek out a qualified engineer, which is exactly what i've done, but seems you don't always get the right answer.

 

[Johntheo5]

First, depress the schrader valve at the air end, assuming its accessible, if water sprays out for say 3 minutes or so, then the diaphragm has failed and the EV is full of water so the PRV will lift when cylinder is reheated. If no water and no pressure then the UV cylinder must be depressurised and drained down below the level of the EV bottom, the EV is then pressurised to 2.8/3.0bar and tested for any leaks, the UV cylinder is then refilled and the tundish inspected for no signs of PRV leakage, the EV outlet does not have to be repositioned to the cold feed but as pointed out, ideally, yes.

 

[Madrab]

thanks for this

how are each of these potential problems(compromised membrane and temp/pressure relief valve) diagnosed and resolved? obviously i am not qualified, you're always told to go and seek out a qualified engineer, which is exactly what i've done, but seems you don't always get the right answer.

Unfortunately you seem to have got a bit of a numpty that TBH shouldn't be G3 qualified if that's what he's said to you. Sounds to me like he trying to make up work and make the job more worthwhile to him, hear it happening all the time.

As @Johntheo5 suggest the EV needs tested to see if the membranes compromised, if it isn't compromised then it needs re-charged. That is the primary reason that a UV cylinder tends to drip @ the tundish as the EV cannot absorb the expanded water, the pressure rises and the Pressure relief valve (PRV) lifts.

If that's all done and it is still dripping then it time to look at the TPRV or the PRV for a fault - they can be disconnected from their tundish connection to see which one is dripping, then if the EV is all fine the one of both valve(s) would be replaced.

 

[unrulyg]

thanks for everyones replies...update:

i had already given him the go ahead prior to opening this thread and reading the replies.

he arrived today, removed and replaced the old expansion vessel, and put it in the "correct" location with new piping, replaced the leaky flue, and serviced both the vented cylinder and the boiler.

he said the old expansion vessel was gone, said that it was full of water..not sure what to believe, but hey ho.

so far so good, no more dripping at the tundish and he seemed a nice chap.