Noisy vibration from Ravenheat CSI Primary

[andy72]

Hi,

I've been looking in this forum for similar problems but can't find one so I'm posting this question.

I've a Ravenheat CSI primary condensing boiler feeding a 180Ltr thermal store. Recently the boiler has started to vibrate at various stages whilst heating the water, sounds like someone is drilling a hole in the wall with a hammer drill sometimes ! Yet sometimes it's so quiet I wonder if it's running....

I've checked everything I can think of in the boiler, even removed the heat exchanger and condensing heat exchanger and flushed them through, which revealed nothing, and made no difference.

The system has been treated with X200 and a descale treatment. Required amounts were used, e.g. 3 bottles to cover the tank + rest of the system.

Despite the noise, the boiler is actually working fine. Reducing the gas pressure down to the minimum setting (2mbar) doesn't remove the problem, but does make it a little quieter.

Everything inside the boiler is secure, no loose parts that I can see. My only theory at the moment is that the main heat exchanger is resonating when the boiler is running. But proving this when the front cover is on is easier said than done....

Just wondered if anyone had seen/heard a similar problem and could suggest some possible things to try.

Thanks

Andy

 

[Slugbabydotcom]

2 main suspects

1 Gas valve solenoid/s
2 Fan

I know things get hot in there so this way is not always practical, but if you can hold or perhaps push something solid such as a hammer shaft against suspect parts then you may be able to feel for the source of resonance. You know you could be on the right track if the resonance stops or is strongly felt.

 

[andy72]

I'll give that another try as I'd already tried that and came up with nothing - virtually all of the housing seems to be vibrating, and 'cos you can't open it it's not possible to try it on individual components.

However, nothing to be lost in checking the fan with the boiler shut down, maybe a bearing problem ?

One thing that is strange is that *sometimes* the vibration stops when the temperature gets much higher. Most of the time when the boiler is running the vibration is present, and the input temperature is less than 60 deg C, although for the last few minutes the temperature goes up to about 70 deg C which usually causes things to quieten down a little.

Andy

 

[Slugbabydotcom]

Have come across an instance where the noise from the pump travelled through and actually sounded louder at the boiler. It is possible that the pump could be a source of resonance even though it is remote.
How old is the heatstore?

 

[andy72]

Heatstore is just under 6 years old. Reason I don't think it is the pump is that after the boiler shutsdown the fan runs for a few minutes, and it's very quiet, no noise at all. The pump is next to the tank on the first floor, feeding the boiler on the ground floor.

Andy

 

[Slugbabydotcom]

Get a drop of oil on the fan bearings to see if there is any improvement.

I agree that the pump isnt as likely as the other two but it is something that I would be looking at as well.
Do all of your rads work ok?

 

[andy72]

Oiled the fan last night, no change, unfortunately. Radiators all work fine but then I wouldn't expect them to be causing the problem. The thermal store feeds the central heating independantly of the boiler, boiler heats the store, radiators take heat from the store. Same with hot water.

I'm sure this is something simple somewhere, I even looked at replacing the heat exchangers. At over £300 each that is a no-go - I could buy a replacement boiler for that !

Andy

 

[Slugbabydotcom]

Radiators all work fine but then I wouldn't expect them to be causing the problem.

Me neither but if the downstairs rads were slow to heat it could be a symptom.

Please bear with me and try to answer the following questions even though some may seem irrelevant or obvious

How many rads do you have and of these how many are fitted with TRV's?

What is the make and model of your heatstore?

Are you sure the valves underneath the boiler and on the heatstore are all open fully or at least as they should be?

There should be an anti gravity valve on the boiler flow to the heatstore. Do you think it is possible that this is where the noise is coming from or are you still adamant about the heat exchanger/s?

Have you had any pressure problems with the boiler and had to top up the system often?

What speeds are your pumps set to ?

There will be a by-pass on your heatstore. What is this set to?

Can you tell me which stage of operation the heatstore is at when the noise occurs.
There are as you know 3 stages of operation :-
Primary flow to heatstore
Central heating
Domestic hot water
It would be helpful to know during which stages of operation the noise occurs. I suspect it will be one or more combinations of the above with the DHW function least likely or indeed relevant.

Has the boiler ever shut down on overheat so that you have had to remove the screwcap and press the reset button?

I appreciate your rather good description of the noise here and when it occurs. You are my eyes and ears and I know its difficult to elaborate but could you try and would you describe the noise as kettling - boiling or perhaps a more mechanical noise?

Dont go throwing parts at it just yet. The heat exhanger/s and indeed the boiler could be showing symptoms of another fault.

 

[andy72]

Have a look at this link

http://www.heatweb.com/systems/files/Specification 1605-5.htm

It should answer some of the questions.

I think you'll then see why anything to do with the central heating is irrelevant - the boiler only ever heats the water in the store, from which the central heating and HW then take their water. The boiler makes a noice when it's heating the store - regardless of what cooled the store in the first place.

There's never been any pressure issues or boiler overheat tripping. No water is lost, and no other leaks anywhere else.

There is a definate reduction in noise, almost silent, when the temperature to the boiler exceeds 60 deg. C. Weird !

When the boiler was installed I fitted a lock sheild valve to the flow and return 22mm pipes. They are fully open. There is no anti-gravity valve, again, don't think it's needed. When the system shuts down the pipes cool as expected which would indicate no water flow from the thermal store.


Andy

 

[Slugbabydotcom]

There is a definate reduction in noise, almost silent, when the temperature to the boiler exceeds 60 deg. C.

This points to a temperature differential problem. I see a blending valve #41 on that drawing, top right. It appears that this valve sorts out the ratio of hot water from the top of the tank to the cooler water from the bottom of the tank. I would say it could need adjusting so that more hot water goes down the return to keep the temperature differential right at the boiler.
Can you answer my question about the pump speed at least with regards to the primary pump#27

 

[andy72]

Boiler is a condensing boiler, so ideally the temperature needs to be kept reasonably low, I aim for about 50, but then it's noisy, so 60 is better.

Concerning the pump, it's been set on first setting, and second setting. I've then tried different gas/burner pressures at each setting, the lowest setting of 2mBar gives a pretty low output, but makes the noises of higher frequency. I've had better results with a higher gas setting, currently pump is set to II and gas pressure is set to give a 15 deg temperature rise.

The boiler manufacturer states a maximum temp. rise of 20, so it's well within range.

Pump is Grundfos 15/60.

 

[Slugbabydotcom]

When you use a primary boiler in conjunction with a heat store a lot of the normal rules for setting up a boiler in a conventional system are thrown out of the window.
I know your boiler is condensing and it works more efficiently at a low setting but for it to work with the heatstore it should be set to maximum or at least [my suggestion] 77ºC. This should give a mean temp of 67ºC between 'burner on' temp of 57ºC and 'burner off' temp off 77ºC
I would set the boiler output to 68000btu [7.5 mb]if the primaries are 22mm and max [10.5mb] if they are 28mm

According to these rather scant instructions, which were the only ones I could find, they suggest that the primary pump be set to speed 3.

They also suggest a temp diff of 10ºC. I would aim for this rather than following their implication that this should be as per the boiler manufacturers instructions.

It would be a good idea to get hold of the MI's to see the rest of their requirements. Their email address is at the link you posted here earlier.

A 6 year old pump is probably at the end of its lifespan now and will probably need changing soon anyway.

I am fresh from the experience of being tortured by a similar set up, Same boiler on LPG with a different heatstore and an intermittent fault which would only occur after I had got my tools in the van and got 2 miles down the road.
The common denominator in this case was the act of putting the cover on and leaving it for 10 minutes during which time the latent ailing pump reached its critical temperature and started to slow down resulting in overheating.

 

[Agile]

I would suggest you use a stethesoscope or listening stick to identify the source of the noise.

You need to determine if its the combustion or water flow causing the problem. Perhaps you have already mentioned that it continues if the burner is not on?

A condensing boiler is not as efficient as it might be with a thermal store unless you operate it in conditions when the thermal store is not so effective.

Tony

 

[andy72]

Tony: Problem only occurs when burner on, when pump is in overrun, there is no noise at all. As for using some sort of listening device, I thing this would be difficult as the whole (sealed) part of the boiler seems to be vibrating. Ideally I want to be inside this area, but I can't then fire the boiler. Bit of a catch 22 situation....

Slugbabydotcom: I may have given you misleading information before. When I mentioned boiler temperature I meant temperature of the blend mixer going to the boiler from the store (No.41 on the diagram). The boiler thermostat itself is on maximum.

Reason for having the blend mixer set to 50 deg C was that it would keep the boiler condensing for as long as possible. Then once the store got above 50 the tempearture would slowly rise until such point that the store thermostat cut out. Setting the blender too high does cause the boiler to cut out, resulting in the boiler cycling unneccessarily.

Have a look here http://www.heatweb.com/systems/files/Install 1605-2.htm This is for a virtually identical system but with an integral F&E tank. Everything else is almost identical.

Given that I've adjusted so much recently, just to confirm the following setup is Boiler Pump at setting II, which gives a temp. diff. at the store of about 14 deg. C. The current gas pressure is 2mbar, which according to the manual gives net heat input of 44500 BTU and output of 40100 or 45700 condensing. The mixer is set to 50deg.

The store is on the first floor, boiler ground floor. The height difference between the boiler flow into the store and the bottom of the boiler is 2.3m. According to the Grundfos specs. for this pump with a head of 2.5m, it should manage a flow rate of .48 litres/second. At setting III, 0.64 L/s.

This is where it gets interesting.....

According to my calculations, allowing for a loss in flow of 20% due to pipe length and valves etc., we would have 1382 l/hour. At 40100 BTU/h we would have a tempearture rise of 13.2 deg F which is 7.3 deg C. And I'm getting 14.....?

Working back the other way, it would suggest that I'm getting an actual flow rate of 723L/h or 0.20L/s. This is 42% of spec.! Could this be right ? Or is the pump knackered ?

Either way, it still exceeds the boiler min. flow rate of 503L/h according to the manufacturers information. And a 14 deg. C rise will work fine....

This is getting more interesting by the minute....

Andy

 

[Slugbabydotcom]

I see three possible causes right now

1 Fan
Ok you have lubed it and it can virtually be written out by your description of the noise. With the cover off and exterior doors locked and windows closed in the house you can see whats going on in there by removing the red tube from the flue restrictor and very gently blowing down it after the fan starts. This will operate the microswitch and the boiler will light.

2 Gas Valve.
This is a little suspect. It has after 6 years of working a heatstore probably used most of its 300000 ish operations up. A chattering solenoid could perceivably sound like a hammer drill but I am sure you would have noticed that when you took the outer cover off. The noise caused by them is usually described as a bit 'tinny'. By using a large screwdriver or something similar as a stethoscope maybe you could have another listen to it.

3 Reduced primary flow resulting in kettling.
To put you in the frame of mind for solving this think of reasons why the boiler might get too hot
Suspect number one here is the pump. They do a lot of work on heatstores and don't last as long IMO as they would on any other type of system.

I'm sure this is something simple somewhere,

Another major pointer here is that you have it set below the manufacturers recommendation. It should be set to 3! This would reduce the cycling of the boiler as the temperature increase is lower in one pass.

By reducing the temp increase through the boiler you are bringing it well within the recommended difference stipulated by the manufacturer this should allow you to increase the rate of gas being thrown at the water passing through the heat exchanger allowing your store a faster recovery time when water is being drawn from it. This works against the good pump flow and a 'sweet spot' should be found by juggling between the primary blending valve, gas rate and a little bit of control stat where noise is at a minimum.

When the boiler was installed I fitted a lock shield valve to the flow and return 22mm pipes. They are fully open.

Do these allow a full bore flow through them? Why did you fit them? They could be causing a restriction which is reducing the efficacy of the pump. The only valves you should have on that circuit are the ones on the boiler or recommended for the heatstore.

Your calculations impressed me, however they do not allow for real life factors such as an apprentice shoving half a roll of solder into a pipe because he never cleaned a fitting properly or an installer who is slap happy with PTFE tape and wrapped so much round a thread that it actually created a blockage.

Check the boiler flow temperature at the boiler just before it cuts out, try taking it just back off the max. I dont know what you are using for a thermometer but I find 'K' types like this to be the better than pipe stats. I am suspecting that the control stat could be on its way out here and not shutting the boiler off as early as it should.