Vaillant boiler noise like a motor from system

[Henryk]

I have had a new Vaillant combiboiler Ecotec 838 fitted together with new copper central heating pipework. The whole system is new. It works well except for a noise like a motor coming from the system from time to time for about 10 minutes and then stops. It is difficult to say where the source is but could be from the boiler. When hot water is called for it stops, and then resumes once hot water tap is closed. From cold in the morning the boiler is silent until it reaches near the set temperature on the external thermostat. Can be about 1.5 hours. The noise then starts on an intermittent basis. I am only putting on 2 or 3 radiators on at a time as we don't need to heat up the other rooms. We have 3 bedrooms, 2 reception rooms, kitchen/diner and 1 bathroom upstairs. The bathroom has a towel rail with on/off valve which I leave on. I understand the boiler has a modulating feature which adjusts the pump flow rate to suit the number of boilers turned on. Would anyone be able to offer advice on how to eliminate the noise sounding like a motor. We do not leave the heating on at night as the noise wakes us up.

 

[CBW]

I would check a trv, but after contacting the installer to sort the issue 1st.

 

[Mike13]

That was my thought too, a TRV being run "backwards", some complain at close to shutoff condition when the flow inlet is the wrong way round.

 

[Henryk]

Thank you. The installer did come back and said it could be a TRV valve. He took one of the valves off and asked me to run it like that the next day and see what happens. I also have to leave the bathroom on off valve on permanently. I did this and had another couple of rads on 2. This did not make the noise for longer but after a couple of hours the motor noise came back intermittently about 10 minutes each time. The room without the valve became very hot and the other 2 open rads did not heat up very much. The thermostat was in the room with valve taken off. He also said I should leave about 4 rads on 3 all the time. However, we want to save energy and only want to heat up the rooms we are using. This is the way our previous combi boiler worked and we had not trouble with noise. Surely we should be able to control the rooms we wish to heat up with the TRVs and Thermostat without the noise.We would appreciate any views on this.

 

[Mike13]

the cure is either to swap the offending TRV(s) to the other side of the radiator, or to swap the whole send and return pipes at the boiler, another way is to change to a TRV that is is not direction sensitive. leaving it like that is wrong.

 

[Mister Banks]

Thank you. The installer did come back and said it could be a TRV valve. He took one of the valves off and asked me to run it like that the next day and see what happens. I also have to leave the bathroom on off valve on permanently. I did this and had another couple of rads on 2. This did not make the noise for longer but after a couple of hours the motor noise came back intermittently about 10 minutes each time. The room without the valve became very hot and the other 2 open rads did not heat up very much. The thermostat was in the room with valve taken off. He also said I should leave about 4 rads on 3 all the time. However, we want to save energy and only want to heat up the rooms we are using. This is the way our previous combi boiler worked and we had not trouble with noise. Surely we should be able to control the rooms we wish to heat up with the TRVs and Thermostat without the noise.We would appreciate any views on this.

All TRV valve bodies have an arrow showing direction of flow. Check these are all correct and on the flow to the radiator not the return.

If only 1 out of 3 radiators get hot with all the TRV’s fully open then the radiators need balancing.

 

[Henryk]

Thank you for your help. All the radiators get equally hot when they are fully on. I have checked on which side of the rads the TRVs are on. I found that 3 of them are on the return side, the rest are in the flow side. As far as I can tell the 3 on the return side create the noise. A slight tweak of the setting eliminates the noise straight away for about 10 minutes and then comes back and then a further tweak is necessary. This happens after the heating has been on for a while and reaches temperature. However, the Honeywell VLT120 valves are new and are bidirectional, with an arrow pointing one way and another arrow the other, so this should not be the cause. The Heating Engineer said it could be the boiler pressure is too high causing the valves to vibrate. Any thoughts on how to fix this would be greatly appreciated.

 

[Mike13]

well what happens is that the dynamic pressure from the pump is either pushing against the nozzle, or is helping it to close. the actual static pressure of the water applies equally to both sides of the valve and is absolutely irrelevant for normal boiler pressures. The only fix is to swap the TRV over to the other side for the three making the noise. Either you make the installer fix it or you do it yourself. Nothing else will change the situation without spending more money on better TRV's

 

[Harry Bloomfield]

I would check a trv, but after contacting the installer to sort the issue 1st.

Simply going around the system, and turning up each TRV, will identify which TRV is causing the noise, when the noise is apparent. When the noise stops, you have found the problem.

 

[CBW]

Simply going around the system, and turning up each TRV, will identify which TRV is causing the noise, when the noise is apparent. When the noise stops, you have found the problem.

Not always the case, but thanks for teaching me to suck eggs.