Water hammer when hot water comes on, following heating.

[bhunachicken]

I'm experiencing a water hammer when my hot water comes on, following on from the heating.

My hot water is on a timer, to come on twice a day to fill a hot water tank. If I have my heating on in between, then when the hot water come on there is a nasty, loud water hammer.

The hot water / heating is controlled by a motorised valve, and a pump.

I thought I had fixed this last year, by reducing the pump speed to the lowest setting. It certainly helped, and the bang was reduced to something almost inaudiable, but several months later the loud bang has returned, even at the low setting.

I'm at a loss to understand why this is happening. I would expect a water hammer to occur if the motorised valve changed at all, but it only happens for the hot water, following the heating being on. It's particularly annoying, as the hot water comes on at 6am, so I am currently being woken by the loud bang.

In addition, and this might be unrelated, but whenever I have my boiler serviced and the magnetic filter is opened up, the entire heating / hot water system will air lock for several hours (it once took 3 days to clear..!). Could the hammer be related to air getting into the system?

 

[CBW]

The timer doesn’t fill your hot water system, it just heats it up. I would say either the motorised valve is making a noise or the float valve.

 

[bhunachicken]

I would say either the motorised valve is making a noise or the float valve.

Somewhat annoyingly, the Honeywell current one (a Neomitis MTV322) has been in place for 2 years, since the previous value broke down. However, the previous one also caused a similar water hammer.

Is the float valve located in the valve or some place else..?

EDIT: it's not a Honeywell, it's a Neomitis MTV322.

 

[ianmcd]

If your pump is fitted as it was supplied then it is upside down, that would cause the noise, have a look on the actual body of the pump and you will see a direction arrow, if it is pointing upwards that is your problem

 

[bhunachicken]

It's difficult for me to see the arrow, due to the proximity of the pump to the adjacent water tank. If it's on the left-hand side, which according to illustrations I've seen, it should be, I'll need to get someone to remove it to check the arrow.

If your pump is fitted as it was supplied then it is upside down, that would cause the noise

The pump has been fitted as seen in the photograph. It was fitted this way 12 months ago. I was having a boiler service performed, and the system airlocked. The lad from the firm serving it fit this new pump as he told me the existing pump was dead, and was incapable of shifting the blockage.

if it is pointing upwards that is your problem

Why is this wrong? The boiler is directly beneath (in the kitchen, and this room is above it). Which way should it be facing?

 

[CBW]

I don’t think the cylinder is in the way as it’s possibly on the right hand side. Looking at the photo again, are the pump valves fully open?

 

[bhunachicken]

I believe I can see the arrow. The housing behind the main unit is red, and I was looking for an arrow on the main black body, but it looks as though the arrow is pointing down. Again, quite hard to see, due to how snug everything is in there. I'll try for a better look when there is more natural light.

Edit: incidentally, my issue sounds a bit like this post here, from 2011: https://www.diynot.com/diy/threads/grundfos-pump-speed-setting.297863/

 

[ianmcd]

I believe I can see the arrow. The housing behind the main unit is red, and I was looking for an arrow on the main black body, but it looks as though the arrow is pointing down. Again, quite hard to see, due to how snug everything is in there. I'll try for a better look when there is more natural light.

Edit: incidentally, my issue sounds a bit like this post here, from 2011: https://www.diynot.com/diy/threads/grundfos-pump-speed-setting.297863/

The arrow on the body must point down the way, if it points up the way that is your problem