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.

 

[dylan_t42]

Thanks for all the input - will be out today, so going to leave these here & pickup sometime next week…

"We can provoke the thud/dunk noise by manually re-opening the DHW two-port ,,,
Do you mean when you open the 2 port while the CH is running or after the CH has stopped?

Happens with CH both on & off - our current guess is that pressure is built up against the DHW valve in the de-aerator ^ released as the DHW zone valve opens.

This MPV must have had its wiring modified, otherwise with both HW&CH requested & both stats calling, then it would go to mid position

Yes - rewired through new control unit which goes DHW-only for the duration of the hot water cycle, which we found odd but only lasts 10-15 mins

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

For yesterday’s checks, this seems to be the sequence but can’t absolutely check the MPV position visually

You might ask someone to watch the EV pressure gauge for any fluctuations, after checking the above, on change over, both ways.

The pressure is pretty steady over the day for just CH, only slightly higher during DHW

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

Baxi Solo PF3 & some sort of Grunfoss

Have you any wiring diagram for this setup?

That’ll be hard to reverse engineer :-{

And perhaps a sketch of the installation

Will see what we can do next week.

TTFN !

 

[Johntheo5]

Happens with CH both on & off - our current guess is that pressure is built up against the DHW valve in the de-aerator ^ released as the DHW zone valve opens.

Is this de aerator a Spirovent type and where is it installed?

 

[Johntheo5]

I found these schematics in my archives, I put them together, two of them are the same normal Y Plan (no two port) but one is a Flameport, the other is just a different schematic.
The Y Plan with 2 port for the UV Cylinder is a Flameport schematic and it seems reasonably clear that the 2 Port is controlled only by the cylinder stat, neither the boiler or the pump should run until the 2 port is fully opened as its end switch starts/stops them.
If HW is demanded with CH on then the boiler/pump should stop as soon as the MPV starts moving and not restart until the 2 port is fully opened?.

 

[Madrab]

Yes - well, the boiler may shut down but if the pump is being controlled by the boiler, which it really should be, then it will continue on the overrun.

Typically a 2 port would be placed upstream of the 3 port Mid to the coil and be entirely controlled by the HL stat. It is part of the mandatory safety features when putting an unvented onto a Y plan. Though TBH it is much easier just to remove the 3 Port and turn it into an S plan that fails to safe. When coming to PDHW then that's different again but normally no other valves would be needed as the 2 port in that configuration would always fail to safe, as in an S plan.

Not sure if that may be a better idea for this system. TBH, I hate when systems are 'jury rigged' to alter how something normally works, in the case of the 3 port Mid valve. It may be easier to take it back to basics, remove the 3 port, introduce a NO on the CH side and standardise the wiring as a PDHW system.

Would make things so much easier and at least once the system was standard, if the valve still knocks then it has to be the valve, wouldn't be the first time I've had a faulty valve out of the box

 

[dylan_t42]

Is this de aerator a Spirovent type and where is it installed?

Yep - SpiroTech RV2 Deaerator - fitted between the Wilo pump & the three-port/MPV.
Thanks for the schematics John - will compare & advise.

Yes - well, the boiler may shut down but if the pump is being controlled by the boiler, which it really should be, then it will continue on the overrun.

I’d note we can reproduce the noise both with & without the pump running, so there must be a static pressure difference across the DHW two-port that’s being released when it opens?

…just to remove the 3 Port and turn it into an S plan that fails to safe…
Not sure if that may be a better idea for this system…
Would make things so much easier and at least once the system was standard,

After reading back a bit, I think I agree.

if the valve still knocks then it has to be the valve, wouldn't be the first time I've had a faulty valve out of the box

Though it may be simpler to just replace the two-port to start with?

 

[Madrab]

I’d note we can reproduce the noise both with & without the pump running, so there must be a static pressure difference across the DHW two-port that’s being released when it opens?

You would think so, if there is a pressure differential and not just a mechanical valve issue.

Though it may be simpler to just replace the two-port to start with?

It may be yes and as you are familiar with the system and it's nuances then great, could be the way to go. TBH though it is a bit of a hybrid, the re-wiring of a mid pos valve to work like that is really just a work around as it leaves the system with wiring that could cause a bit of confusion if someone wasn't experienced with it. if reverting things to a standard is achievable then I would suggest it might be a good place to get to.

 

[Johntheo5]

You probably have, but ensure the Spirovent which is uni directional is pointing the "right" way.
Also next time the system is in CH only, (with 2 port closed), check that the pipe say a foot downstream of it is cool/cold, then latch open the 2 port and see does the pipe still stay cold, this will prove that the MPV is going fully over to CH only, even though still should't cause your problem.

If the MPV is staying in its "last port of call", say after CH mode above, then the water will be trapped between the MPV and the 2 port so just maybe building up a bit of pressure due to heat or whatever? but there must be hundreds of non PDHW that shut down in this fashion and don't have this problem.

 

[dylan_t42]

You probably have, but ensure the Spirovent which is uni directional is pointing the "right" way.

It is & we had ;-}

Also next time the system is in CH only, (with 2 port closed), check that the pipe say a foot downstream of it is cool/cold, then latch open the 2 port and see does the pipe still stay cold, this will prove that the MPV is going fully over to CH only,

It does - which is good to know.

even though still should't cause your problem.

I'd agree - but it did bang while latching the DHW two-port open to do the flow test :-}

If the MPV is staying in its "last port of call", say after CH mode above, then the water will be trapped between the MPV and the 2 port so just maybe building up a bit of pressure due to heat or whatever?

The DHW activation sequence opens the two-port before the MPV moves between A/B...so the pressure is arising between the valves. Wonder if we can provoke it by opening the MPV?

but there must be hundreds of non PDHW that shut down in this fashion and don't have this problem.

So at least there's a hope that we can arrange ours likewise!

 

[dylan_t42]

I'm happy with where we've got to with all the input & advice.

We now have something that we can demonstrate on demand & show our working, before we start draining down & swapping/rearranging components.

Thanks @dilalio, @madrab, & @johntheo5 - your help is much appreciated.

 

[Johntheo5]

So can you confirm (again?) that if DHW reheat was last requested and then subsequently requested again then no noise.

Can you manually vent that Spirovent?