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Open vented fully pumped oil fired system. Works well but occasionally (every few days or do) loud throbbing noise from pipes directly above boiler. Goes away if system switched off and then immediately on again. New pump and no benefit from replacing zone valves. Any ideas gratefully received
 
Open vented fully pumped oil fired system. Works well but occasionally (every few days or do) loud throbbing noise from pipes directly above boiler. Goes away if system switched off and then immediately on again. New pump and no benefit from replacing zone valves. Any ideas gratefully received

You need to provide more details of the system.

As a first guess, you might be describing the sound of pump overrun through a bypass loop. How long does it go one for if you don't switch the boiler off and on again? If the automatic bypass valve is too tightly closed you may be overloading the pump?
 
Thanks for your initial replies and apologies for not including enough data. The boiler is a POP Firebird 120 with a Riello RWB burner. I've attached files to illustrate the set up. The horizontal pipework after the bifurcation above the pump is for the hot water and the vertical for the heating. I've also attached an audio file to illustrate the noise. The noise only ever comes after the system has been on for an hour or so. When the noise is present it seems to be worse in the red section on the side of the pump but the pump is completely quiet when the noise is not present so I don't know whether the noise is centred there or just being echoed from there. I haven't let the system run when it's making the noise so can't answer the specific question you pose about how long it lasts for. Many thanks for your further help.
 

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Does the boiler run continuously for one hour without cycling and when it does cycle off does the pump run on continuously which it should except both zone valves closed.

When both zone valves close does the pump run on (overrun) for a minute or so and then stop.

Is the noise only apparent on CH only?

What make/model/mode/setting is the pump.

Is the arrow on the pump pointing upwards.
 
Thanks for your reply.
The boiler cycles on and off right from the start so, no, it doesn’t run continuously for an hour to start with. The pump runs continuously when the boiler cycles off.
The pump shuts down immediately both valves close.
The noise can appear either on ch or hw or both.
Pump is Wilo RS25/6 3 ku p. Setting 3. Don’t know how to determine the mode.
Can’t find an arrow on the pump but installed professionally so hopefully done properly.
Just been out to the garage to check some of the queries you raise and the system is running almost silently (except for when the boiler is cycling on). This is the frustrating thing where everything works fine for long periods of time ie days then suddenly the noise starts!
 
Just feel the left hand pipe, if its hotter than the right hand one then the pump is pumping in the correct direction.
Also that left hand pipe should be coming off the top side of the boiler with the right hand one returning to the bottom of the boiler.

I have a SE 20kw Firebird with the pump on the return and if the boiler re fires after say 10/15 minutes after zone valves shut then re open you can hear the water burbling for a few seconds in the flow pipe, I have measured this temp at 90/100C (boiler SP 70C). Obviously if boiler just cycling normally then no problem as circ pump running continuously.
The recording might sound a little like cavitation so maybe reduce pump speed to 2 and/or if boiler SP temperature 70C or more reduce to say 65C.

You also said that the boiler cycles right from the start, from a cold start it should run continuously for 20 to 30 minutes until system contents up to temperature, presume yours does likewise.
 
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Just looking at pictures of your boiler/pipework. One thing strikes me as odd you say in first post you have a open vented system just how is cold feed and open vent connected to system?
 
There's a pipestat on one of the pipes so maybe a gravity HW system with the vent a continuation of the top entry to the HW cylinder coil. and two CH zone valves, upstairs/downstairs.
 
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When you go through your OFTEC course they do, at least when I last went through it state any pipe stat wired in series with a frost stat should be installed on the CH return so you emitt the heat into the heating circuit momentarily. It's possible it's been wired in on the HW circuit though if it is related to a frost stat. As exedon says though where is the vent and cold fill situated?
 
The furthest right side pipe could be the boiler return and maybe the cold feed from the F&E tank is piped into this, it looks like the only unrestricted (apart from the gate valve) path. I don't think it could be classed as a OV though, glad there's a PRV on the boiler.

Here is the frost stat/pipe stat schematic, recommended that the pipe stat, installed on the boiler return is set (to open) at 25C.

1635838636040.png
 
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Main reason I mentioned it is we have come across a fair number of systems 'converted ' to fully pumped by simply using existing gravity system without modification!.
Generally called to them because system noisy some rads not working or boiler leaking.
 
Here is the frost stat/pipe stat schematic, recommended that the pipe stat, installed on the boiler return is set (to open) at 25C.

The pipe stat is set to a low temperature, around 20°c yes just to take the chill off the boiler. It's wired in series with the frost stat and should be wired into the CH by-passing the room stat. This takes the chill off the boiler while using minimal fuel. If there was no pipe stat the boiler will just cycle putting wear and tear on it and continuously wasting fuel.

I suspect this system has been converted to a sealed arrangement, otherwise without the vent being where it should be the system will be very dirty.
 
Or maybe semi-sealed with a NRV on the cold feed, the vent blanked off and a E.vessel installed somewhere, very common around here as they are considered more forgiving than the fully sealed systems as long as the EV pre charge is kept to 0.5bar.
 
Yes it is a possibility and judge by the quality of pipework I imagine the system is a maze.
 

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