Popcorn noise from boiler

[LittlePlum2]

Bypass in 22mm is wrong innit? should be 15mm, is that an auto bypassvalve I`m lookin at also?Might be worth getting someone in who has a clue friend maybe ask some questions of the `engineer` who fitted bypass.

 

[D_Hailsham]

Not sure if your 'Have you balanced the system?' question is actually part of your signature but, for the record, yes.

No it's not my signature. I asked because you mentioned trying different pump speeds. A correctly balanced system will use a lower speed than an un-balanced one.

Many instructions for balancing a system are incorrect. Read the link I posted to find out how it should be done.

 

[iep]

Yep, balanced the system using your guide (very useful, thanks).

The only oddity I noted was that, even on pump speed 2, the temperature drop across the system (meaured at the send return pipes of the boiler) was only 6 - 7 degrees.

This suggests to me that the flow rate is too high. However, the manual for the grundfos pump that I have (see links in first post) suggests that, for the ideal flow for the boiler (23l/m, 0.38l/s), the pump is only generating 1.2m of head. Given the boilers resistance of 0.8m (taken from diagram 2.2 in the boiler manual, see link in original post), this leaves only 0.4m of head to drive the system.

If I were to reduce the pump speed to setting 1, the pump apparently will only provide about 0.1m of head at 23l/m. In this case, the flow will obviously be far too low for the systme ot operate safely.

I guess I could try speed one and check that the temp drop across the systme approaches something more like the ideal 11 degrees but I am worried that this might damage the boiler. What do you think?

iep.

 

[transam]

I assume that the boier does not kettle ??? when only hot water is programmed e.g h.w only ??? & the bypass is not operating ???

 

[iep]

No, the boiler does not kettle at all. Provided that either or both of the zone valves are open, the boiler runs very quietly.

The issue is specifically limitted to the case where the cylinder and/or room thermostats switch the system off and the pump overrun function becomes active.

iep

 

[D_Hailsham]

The only oddity I noted was that, even on pump speed 2, the temperature drop across the system (measured at the send return pipes of the boiler) was only 6 - 7 degrees. This suggests to me that the flow rate is too high.

I can understand why you are suggesting that, but it may not be necessarily correct. It could be due to the fact that, now it is warmer(???), the radiators do not have to give off so much heat. The boiler is being controlled by the room thermostat, it never reaches the temperature set by the boiler thermostat. You could allow for this by turning the room thermostat right up so the boiler is running continuously while balancing. The boiler thermostat also needs to be at max.

You should balance the system so the drop across each radiators and across the boiler is the same and as near to 11C as possible. You may not be able to achieve the "ideal" 11C as your pump can only work at fixed speeds.

Incidentally, the Boiler manual says that the pump should be in the flow side!

 

[iep]

Hi D_Hailsham. When i balanced the system I made sure that both the room and boiler thermostats were set at their max temperature. I also balanced the system on a cold day when I had let the temp in the house drop to 11 degrees overnight.

I understand that the 11 degree drop is only the ideal, but I was surpsied that I could not get closer to that figure across the whole system. Is there any risk involved in attemprting to run the pump at speed setting 1?

Interesting catch that the boiler wants the pump in the flow side. I thought I'd read that manual pretty carefully but did not spot that requirement. I wonder if this could be causing any issues. I may drop an email to the excellent Glowworm support team.

Cheers,

iep

 

[JohnD]

I'm no expert, but surely if the temp drop is smaller than you want, you should reduce the flow in the system? e.g. by running the pump slower?

 

[iep]

JohnD, what you say makes sense to me and it also stops the popcorn noise (which is the real reason for this post). However, the manual for the pump states that, when in setting 1, the pump is not able to achieve the minimum flow for the boiler.

I'm not sure what damage is likely to occur in this scenario but I'd guess it can't be good.

iep

 

[JohnD]

Ah, I didn't know about that. I have a self-modulating pump and a different sort of boiler.

 

[D_Hailsham]

JohnD, what you say makes sense to me and it also stops the popcorn noise (which is the real reason for this post). However, the manual for the pump states that, when in setting 1, the pump is not able to achieve the minimum flow for the boiler.

At a 6°C differential the flow rate will be about 0.7 litre/sec (42/min). At that rate the boiler resistance is off the scale (see diagram 2.2 on page 8. But the pump would have to be on speed 3 to provide any head at that flow rate. This suggests something wrong: either the temperature measurement is incorrect or the boiler is not producing 17.58KW.

1. How are you measuring the flow and return temperatures at the boiler?

2. Have you checked the gas rate to make sure the boiler is delivering full output? (They can be down-rated if necessary; see table 2 on page 7.)

 

[iep]

I'm using an IR thermometer and have attached matt black aluminium target plates (with lots of heat conductive paste) to the pipes to make for easier measurement. I checked the calibration of my IR thermometer against several other thermometers to ensure it is reliable and accurate.

When operating normally, the send pipe of the boiler is about 75 degrees (I don't run the boiler at max temp) and the return is at about 69degrees. This measurement correlates with the inlet and outlet ends of the radiators.

As soon as the zone valves close and the system goes into pump overrun mode, both the send and return meaure about 73 degrees (as you would expect) which falls off quickly as the system cools down.

I have not checked the gas rate of the boiler. Can this be done by watching the gas meter (providing the oven etc are off) or do I need a specialist tool?

As an aside, I just had a response from the gloworm techinal team (one hour response time, those guys are damned good) and they say that, for the energysaver60, the pump can actually be on the send or return pipe without any effect on performance (though I'll need to move it if I want to install one of their newer models).

Could you explain how you are calculating the temp drop/flow rate that you mention below. Apologies as I think I may have asked you this before (unfortunately, I can't seem to find the post).

Thanks,

iep

 

[iep]

Found it:


Flow rate (litres/sec) =kW Output ÷ (4.18 x Temp Diff)

or

Temp Diff = kW Output ÷ (4.18 x Flow Rate)

Cheers,

iep

 

[D_Hailsham]

I'm using an IR thermometer and have attached matt black aluminium target plates (with lots of heat conductive paste) to the pipes to make for easier measurement.

That's good - at least you are measuring off a surface with the same emissivity all the time.

I have not checked the gas rate of the boiler. Can this be done by watching the gas meter (providing the oven etc are off) or do I need a specialist tool?
Yes, you can check it by timing the gas meter. The calculation depends on your meter (cubic ft or cubic metres) and the calorific value of the gas, which will be on you gas bill.

Assuming the CV is 39MJ/m³, the flow rate will be 20.33/39= 0.52 litre/sec = 0.52 x 3.6 m³/hr. You use 20.33, which is the heat input to the boiler, when gas rating.

So if you time how long it takes for the right hand dial/red counter to make, say 2 or three revolutions you can easily work out the flow rate and convert this to kW input.

Could you explain how you are calculating the temp drop/flow rate that you mention below. Apologies as I think I may have asked you this before (unfortunately, I can't seem to find the post).

No probs

Flow (litres/sec) = Output (kW) ÷ (4.18 x Temp diff)

4.18 is Joules constant aka the Mechanical Equivalent of Heat.

 

[transam]

No, the boiler does not kettle at all. Provided that either or both of the zone valves are open, the boiler runs very quietly.

The issue is specifically limitted to the case where the cylinder and/or room thermostats switch the system off and the pump overrun function becomes active.

iep

If it is not ketteling on hot water only , take out the by-pass valve & put the gate type valve back !!!!