Why Does My Hot Water Circulating Pump Bang When It Starts Up?

[Brian]

I have recently had a new boiler and circulating pump installed keeping the hot water cylinder. I have the hot water timer set to come on for an hour each morning but when the time is reached, a loud bang comes from the pump which can be heard all over the house. Can anyone please suggest what the problem is and how to cure it? If it is not a simple job, I will call the installer back to attend.

 

[SimonG]

Call the installer back, explain to them and get them to put it right.

 

[Scott_D]

Any pictures of your setup?

 

[king of pipes]

Couple of pictures please. Kop

 

[Brian]

Hello Simon. I wasn't going to call the installer if the problem was as simple as something like bleeding the pump. As requested, I attach a picture of the system around the pump. I have a Bosch boiler

 

[John.g]

I have recently had a new boiler and circulating pump installed keeping the hot water cylinder. I have the hot water timer set to come on for an hour each morning but when the time is reached, a loud bang comes from the pump which can be heard all over the house. Can anyone please suggest what the problem is and how to cure it? If it is not a simple job, I will call the installer back to attend.

I have read on here I think that banging can be caused if the zone valve is incorrectly installed, this is a motorized valve, if you look at your cylinder you will probably see one of these valves installed on the coil (flow) close to the top on the side of the cylinder, ensure that the arrow on the valve body is pointing into the cylinder, if the valve is installed on the return (close to the bottom) from the coil then the arrow should be pointing away from the cylinder.
If not this then pump setting may be too high.

 

[RoryD]

There is some kind of obstruction for sure. Wonder if he forgot to open the gate valves either side of the pump?

 

[king of pipes]

As above check zone valves are in correct orientation. Kop

 

[garygvl]

is the hot water timed to come on before the heating in the morning

 

[Brian]

Thanks for all the replies. To answer all the posts in order;
1) The zone valve appears to be the correct way around although the Drayton grey item (bypass unit?) in my photo is upside down.Does that suggest the zone valve is upside down?
2) I will try adjusting the pump.
3) I have already checked the gate valves and they are fully open.
4) The hot water is timed to come on before the heating.

 

[John.g]

Thanks for all the replies. To answer all the posts in order;
1) The zone valve appears to be the correct way around although the Drayton grey item (bypass unit?) in my photo is upside down.Does that suggest the zone valve is upside down?
2) I will try adjusting the pump.
3) I have already checked the gate valves and they are fully open.
4) The hot water is timed to come on before the heating.

You appear to have a three way (mid position valve), from my limited knowledge it appears to be installed correctly, ie "W" is at hot water side and "H" is at CH (port A?) end.

The pump should be pumping downwards so ensure that the arrow on the pump body is pointing downwards.
It should have ~ 10 settings.....Auto Adapt, 3XCC,3xPP and 3XCP settings.
It appears to be on Auto Adapt which judging by a number of posters on here is virtually useless (but still shouldn,t case banging). you might consider jotting down the power in watts and the flow rate in M3/hr for the following 4 modes, all with HW (cyl) only selected, Auto adapt, CC2 (constant curve), CP2 (constant pressure) and PP3 (proportional pressure).
Any of those settings IMO should result in a power consumption of ~ 18 to 25W, flow rate of ~ 0.8 to 1.2 M3/hr, if the auto adapt is only showing <10W or so then forget it.

If the pump is orientated correctly and one/some of the above settings don't get rid of the banging then maybe there is/are non return valves installed somewhere.

 

[garygvl]

the drayton 3 port is banging due to closing from heating setting and moving to hot water setting while the pump is running. common problem, honeywell do it also, due to close proximity of 3 port and pump. need to change drayton 3 port for a danfoss "shoe type" 3 port valve to eliminate problem, attached image show the two differnt valve body shapes, make sure you get the shoe valve

 

[John.g]

Very interesting, Brian stated above that HW is selected on start up in the morning so what you are saying is that either the valve remains in whatever mode was selected on its last shutdown or it defaults to some other default setting, other than hot water, on last shutdown?

 

[RoryD]

Hello Simon. I wasn't going to call the installer if the problem was as simple as something like bleeding the pump. As requested, I attach a picture of the system around the pump. I have a Bosch boiler

It could be a number of things, call the geezer back and have him check it. good luck.

 

[Brian]

I have tried running the heating first then putting the hot water on and the bang does not occur. I am trying to get the installer back now. I will post with the result

 

[garygvl]

I have tried running the heating first then putting the hot water on and the bang does not occur. I am trying to get the installer back now. I will post with the result

It won’t. Run the heating on it’s own, hw turned off, then turn the heating off. Now turn the hw on and it will bang

 

[SJB060685]

the drayton 3 port is banging due to closing from heating setting and moving to hot water setting while the pump is running. common problem, honeywell do it also, due to close proximity of 3 port and pump. need to change drayton 3 port for a danfoss "shoe type" 3 port valve to eliminate problem, attached image show the two differnt valve body shapes, make sure you get the shoe valve

Hi Gary. Can you tell me the difference internally of these two valves that the shoe type eliminates this problem?

 

[garygvl]

Hi Gary. Can you tell me the difference internally of these two valves that the shoe type eliminates this problem?

most heating systems using 3 port valves finish at night with the 3 port held in heating position. if you time the heating to come on first in the morning the 3 port has to spring return to hot water position while pump is running causing, honeywell use a ball, drayton use a paddle, said mechanism to bounce off valve body causing a short bang as it reseats into desired position. the danfoss shoe type closes the port from side to side so the gap closes slower allowing any pressure in the system due to pump flow not to bounce the valve. top 3 pics show difference between the two types of danfoss valve body. last four show valve closing from side to side

 

[SJB060685]

Thanks buddy, I shall remember this

 

[Brian]

Thanks for the replies. M y pump appears to be pumping downwards and set to Auto is showing 45W. As I am no closer to a solution I think I will call the installer back. Thank you everyone for trying to help.

 

[John.g]

45w indicates either a very high head with a moderate flowrate or a very high flowrate with a low head, would suggest trying fixed speed 2 or CP1 (constant pressure), while you are waiting for help. Also there seems to be a balancing (gate?) valve on the cylinder coil return with the wheel head removed, if so you might try shutting this fully and then just open it 3/4 to one full turn and then maybe try the above settings.

 

[Hollinside]

Exactly the same thing in my house - we had a grundfos 25/80 pump and the same type of valve- the 3 port valve stays in its last position until it receives a signal to move. Pump turned on at same time as the pump started and it sounds like a bus crash in there! Newer wilo pump seems to start up slowly and auto adapts and the almighty crash disappeared instantly. If I turn the pump on full power no automatic adapt it can still be replicated though! Try a lower pump setting before shelling out on another valve,

 

[John.g]

Shoud have said try CP2 (not CP1) above.
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Exactly the same thing in my house - we had a grundfos 25/80 pump and the same type of valve- the 3 port valve stays in its last position until it receives a signal to move. Pump turned on at same time as the pump started and it sounds like a bus crash in there! Newer wilo pump seems to start up slowly and auto adapts and the almighty crash disappeared instantly. If I turn the pump on full power no automatic adapt it can still be replicated though! Try a lower pump setting before shelling out on another valve,

Should have asked Brian originally if he had this valve installed before renewing boiler/pump and if so was there still banging, also if he has a 8M pump now installed, IMO 20/25W should reflect a reasonable pump setting selection. I too have 6M Wilo (yonis pico) and on any of its PP or CP settlings it ramps up slowly on every retart and takes - 5/6 seconds to reach its setpoint, I would have thought that the Grundfos would behave in a similar fashion?.

 

[Brian]

John, Everything except my cylinder has just been renewed together with my boiler. I never had any banging before. Not sure if the pump is an 8M.

 

[John.g]

John, Everything except my cylinder has just been renewed together with my boiler. I never had any banging before. Not sure if the pump is an 8M.

OK then, all I can say is that 45W is IMO indicative of excess flow/pressure and reducing this may at least alleviate the problem until you get your installer back, let us know the outcome.