New two-port valve - water hammer on opening

[dylan_t42]

I read it that there are 2 EVs, one on the primary and another on the Megaflo, the boiler is a Vaillant 415, the 4 shows its a heat only boiler (A Vaillant 6 is a system boiler and a 8 is a combi) and has a 18L EV connected in correctly to the external pump inlet.

Yes to all that, other than the EV being connected to return of the primary circuit, not the pump inlet.

There is also a EV connected to the Megaflo, I normally only read about this if the baffle has disintigrated leading to more frequent recharging of the bubble, depending on the precharge & filling pressures of a external EV then this will also cause water shunting between the bubble and the EV but normally only when there is a HW draw off?.

No noise or flow issues drawing HW from the Megaflow but it was needing more frequent recharge so believe the plumber added an EV to alleviate that - whether it was necessary, in the absence of any signs of the baffle disintegrating, is a question for another thread.

It's not specific/clear - as quoted, it's in the same paragraph so it could be read 2 ways,
+
Is this 2 different EV vessels?

Yes - apologies for the confusion

did wonder if additional EV is acting as opposite of shock arrestor. ie shock generator IF its on primaries?

The two EVs are on different circuits:
One on the primary heating circuit, replacing the existing 20yo pressure vessel
One added off the cold feed to the Megaflow hot water cylinder, allegedly to improve flow, and with no issues when drawing water.

I can't remember what I've read now!

You & me both!

 

[Johntheo5]

Yes to all that, other than the EV being connected to return of the primary circuit, not the pump inlet.

No noise or flow issues drawing HW from the Megaflow but it was needing more frequent recharge so believe the plumber added an EV to alleviate that - whether it was necessary, in the absence of any signs of the baffle disintegrating, is a question for another thread.


Yes - apologies for the confusion

The two EVs are on different circuits:
One on the primary heating circuit, replacing the existing 20yo pressure vessel
One added off the cold feed to the Megaflow hot water cylinder, allegedly to improve flow, and with no issues when drawing water.

Have you checked if its a diverter valve or a mid position valve?
Also if you latch open the 2 port valve in CH mode does it still make those noises on C/O to HW?
If it does then that would suggest maybe that its not the 2 port that is the problem at least when changing to HW?

 

[dylan_t42]

Have you checked if its a diverter valve or a mid position valve?

Yes John, we’ve been looking at this:
Honeywell V4073A1039 Sundial Y Plan “Three position diverter valve”
- with a cute little diagram:
Heating/A, Inlet A/B, DHW/B
- which matches the casting letters & the functions of the respective pipes, which is nice.

>Also if you latch open the 2 port valve in CH mode does it still make those noises on C/O [change over?] to HW?
>If it does then that would suggest maybe that it’s not the 2 port that is the problem at least when changing to HW?
Could not get it to make any noise testing this today, although the two-port did unlatch itself each time the cylinder reached its target temp. Seems consistent with what we’ve observed, where the only time we get the noise is when the system changes from CH to DHW as the two-port opens to allow heat into the tank coils.

Which leaves us with with Rob’s question on how the DHW two-port might be making this happen:

Whilst I don't suggest your identification about this 2 port being the source of this noise, isn't correct, just to confirm, can you 'create' this noise on demand? If so, can you be at the valve and hold it when the process is initiated and can you feel the valve itself 'dunking', just to confirm it's definitely the valve.

We can provoke the thud/dunk noise by manually re-opening the DHW two-port *after* the HW cylinder has fully re-heated *and* the CH has been running. The noise only happens once per cycle, for either automatic or manual provocation. It feels like it comes from the upstream side of the valve & we’ll be checking the primary EV in loft again once it’s had a decent run on the CH…

 

[Johntheo5]

Just a few random observations/queries

"We can provoke the thud/dunk noise by manually re-opening the DHW two-port *after* the HW cylinder has fully re-heated *and* the CH has been running"

Do you mean when you open the 2 port while the CH is running or after the CH has stopped?

This MPV must have had its wiring modified, otherwise with both HW&CH requested & both stats calling, then it would go to mid position even if the boiler flowtemp is increased to 70C or whatever, of course this would then mean that the CH would also run at 70C until the cyl stat is satisfied?

One would think the 2 port valve should be fully or near fully open before the MPV moves from the CH to the HW position

You said the EV runs at a steady 1.2bar, I wonder what the precharge pressure is, normally one might have a precharge pressure of 1.0bar with a filling pressure of 1.5bar, On a 18L EV, this gives a water reserve of 3.62L and a final hot pressure of 1.82bar, assuming 100L system contents,
You might ask someone to watch the EV pressure gauge for any fluctuations, after checking the above, on change over, both ways.

What boiler and circ pump did the new boiler&pump replace?.

Have you any wiring diagram for this setup?

 

[dilalio]

Have you any wiring diagram for this setup?

And perhaps a sketch of the installation as @dylan_t42 understands it... Better than all these words imo.