New two-port valve - water hammer on opening

[dilalio]

If pump is not running and, presumably, boiler not firing, there would be no flow through the primaries.

Why would the motorised valves be moving outside demand hours?

All very difficult to diagnose without having hands on it.

 

[Madrab]

I must be honest to suggest I've never had a 2 port actually bang, more of a 'dunk' noise, especially when the pump isn't running. I have had them do that when the pump is running and the valve is either backwards, the valve is badly worn/scaled up or when the system is badly piped and the valve is experiencing reverse flow and the ball lifts then snaps shut again on the spring but it's a very rare thing in all the years I've being dong this.

The only other instance when I've had a banging 2 port was when the valve itself was faulty, the ball wasn't lined up properly/was loose and it produced a 'dunk' when it jumped into it's seat.

 

[dylan_t42]

Responses in slightly random order:

Those Megaflo's could produce noise seemingly from anywhere, when was its air bubble last re charged?

July, when we had the new boiler fitted - there was also an expansion vessel added for … reasons.

best IMO to re charge it, show Mrs T42 how to do it, she will be delighted.

TBF herself specced the original system a couple of decades back & did the leg-work on working out a suitable replacement boiler, so it’d more like her showing me!
But good point - we’ll do a recharge if only to get the flow rate back for the bath :-}

"Wonder what happens if we do that while the pump is running…" Give it a go, no harm in doing so.

Still gives a thump - so not much change there. The vibration definitely came from flow pipe upstream of the two-port, so we’ll have a look at the pipe-clips.

Yes, thats the 6M Wilo like mine, that flowrate of 0.6m3/hr, 10.0 LPM is far too low, change to CP mode" turn the selector clockwise past C3 to the "houses" the selected head will flash each time you make a change, (you can incremantally change the settings in 0.1M steps), so try it at 3.8M and note the flowrate and power, you should get ~ 0.83m3/hr, 13.8LPM and see how it goes.

Interesting to know that we can tweak the “c” speed settings - and found that “c2” already runs at 0.8m3/h so set it at that. We will obviously get faster heat flow around the pipes, but doesn’t that also mean a warmer return temp, so less efficient within the boiler?

 

[dylan_t42]

If pump is not running and, presumably, boiler not firing, there would be no flow through the primaries.

Yes!
But it still bang/thump/rattles when manually opening the DHW two-port, almost flow.
What’s odd is how pressure could be held across the valve, even in the absence of any pumped flow?

All very difficult to diagnose without having hands on it.

Yes - again!

Why would the motorised valves be moving outside demand hours?

To help with diagnosis CH & DHW are now both set to run 06:00-22:00 as it was a bit random previously,

As to “why” the DHW two-port opens, it seems that whenever hot water is drawn off, or the cylinder just cools down a bit, its thermostat reacts to the lower temp & signals the DHW two-port to open, which then triggers the noise.

Yes remote diagnosis is tricky, which is why we spent a week writing down everything before posting on here.

Thanks for the input - will see whether anything works.

 

[Johntheo5]

July, when we had the new boiler fitted - there was also an expansion vessel added for … reasons.

[/QUOTE]

What is the make/model of boiler, is it a system boiler or a heat only boiler with a external boiler with a external EV (expansion vessel) and pump?, the Wilo??
Can you see where this EV is teed into the system, ie, the boiler flow or return, what is the EV capacity, should be written on it.

 

[dilalio]

As to “why” the DHW two-port opens, it seems that whenever hot water is drawn off, or the cylinder just cools down a bit, its thermostat reacts to the lower temp & signals the DHW two-port to open, which then triggers the noise.

Is "part" of the system setup for PDHW?
Or all of it even? But not the 3 port?

What's the exact model of the 2 port?
Is it NO or NC?

May be getting closer to a solution if, as you say, 2 port is motoring via cylinder stat!

 

[Johntheo5]

One would think (hope) that its NC since its purpose is a extra safety feature because the MPV is NO to Port B and the cylinder coil but is interesting all right as to what actuates it.
I did hear of a similar set up but with a system boiler with its EV connected (the normal) to the pump inlet, another external EV was installed when the CH was extended and there were strange sounds just after its installation, eventually it was found that this external EV had been connected at the discharge side of the pump, when it was changed to the inlet side the sounds stopped, can only think that the water when shunting from one EV to the other on start up/shut down was the reason, thats why I ask if the boiler is a system (with a external EV) or heat only boiler as it appears to be with that Wilo pump.

 

[dilalio]

One would think (hope) that its NC since its purpose is a extra safety feature

Being G3, I know that.

Yet components often get installed in error because it looks at first glance like one thing but can be another!

But every detail needs examining and this is what makes remote problem solving difficult because it comes piecemeal and disjointed - I, for one, find it difficult to remember everything that's been mentioned and trawling back through previous posts is beyond what I have time to do to help.

 

[dylan_t42]

Morning - here’s a brief response. Appreciate all the questions & input, and although I can’t now update my original post, will look to collate the info to give a clearer picture…and some actual pictures if that’s useful?

>What is the make/model of boiler…
Valiant ecoFit Pure 415 heat-only boiler with external Wilo pump (now running at 0.8m3/h, 13lpm) on the flow side and the single EV Reflex N18 (litres?) mounted in the loft space & connected to the return. I’d clarify that this replaced an existing EV on the primary. The additional EV was connected to the Megaflow to supplement its internal bubble/baffle (not yet recharged as the flow rate is still good)

>What's the exact model of the 2 port?
Honeywell Home 272848, newly fitted - seems to be “Normally Closed” as that’s where it stays when up to temp or the whole system is powered off - so that’s doing its safety job :-}

>Is "part" of the system setup for PDHW?
Yes, it does a Prioritise-DHW-mode with flow temp ~70ºC and pausing the CH, which generally runs at ~30-50ºC
It’s the switch to DHW after running the CH that initiates the noise, which varies between ‘dunk’, ‘thunk’, & ‘bang’
This doesn’t happen when setup for just one or the other.

 

[Johntheo5]

Since you have PDHW then you don't require a MPV so can you see if the 3 port valve is a MPV or just a diverter valve, don't know if a diverter valve will have Port A&B opened" together briefly when the valve is changing over or not.
Have you tried latching open the 2 port while in CH mode and then request DHW (just turn up the cylinder stat temporarily) to see any difference?

"The additional EV was connected to the Megaflow to supplement its internal bubble/baffle (not yet recharged as the flow rate is still good)"
what vol is this EV and why do you think it will improve the flowrate?, a external EV on any UV cylinder will normally be precharged to 3.0bar or ideally, 2.8bar (seems to help in preventing water hammer?) so there will be no accumulator effect, if a 18L EV is precharge to say 2.0bar then there will be 4.5L accunulated in it at 3.0bar and it will release this in falling to 2.0bar but only if the mains dynamic pressure after the PRV falls to 2.0bar, it will accumulate 6.75L if precharged to 1.5 bar and will only release this if the dynamic mains also falls to 1.5bar. Anyway assuming the Megaflo still has its bubble then this will also affect any accumulator effect.
Did this noise coincide with the installation of this EV?. Do you know what its precharge pressure is?.

 

[Madrab]

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.

Not sure I'm reading this right as it's all in the same paragraph

The single EV Reflex N18 (litres?) mounted in the loft space & connected to the return. I’d clarify that this replaced an existing EV on the primary. The additional EV was connected to the Megaflow to supplement its internal bubble/baffle (not yet recharged as the flow rate is still good)

Is this 2 different EV vessels?

 

[dilalio]

did wonder if additional EV is acting as opposite of shock arrestor. ie shock generator IF its on primaries?
Air bubble on the megaflo is expansion for DHW potable, not primary CH circuit.

 

[Johntheo5]

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.
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?.

 

[dilalio]

I read it that there are 2 EVs

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

 

[Madrab]

It's not specific/clear - as quoted, it's in the same paragraph so it could be read 2 ways, as to what/where the additional EV is. If it was 'An' additional EV was connected ...... then that would be different

Valiant ecoFit Pure 415 heat-only boiler with external Wilo pump (now running at 0.8m3/h, 13lpm) on the flow side and the single EV Reflex N18 (litres?) mounted in the loft space & connected to the return. I’d clarify that this replaced an existing EV on the primary. The additional EV was connected to the Megaflow to supplement its internal bubble/baffle (not yet recharged as the flow rate is still good)