Ravenheat RSF84 vibration problem

8 Oct 2006
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United Kingdom
Hi All,

I'm getting to the end of my tether with our boiler. It has a few of the seemingly common issues people complain about on these forums but nothing that means it dosn't work day to day:

It appears to be kettling in the heat exchanger (kettling is where it sounds like a kettle when heating the CH isn't it?!)
The DHW temperature control won't go past the halfway point without it overheating and cutting off. (I've replaced the CH temperature sensor with no difference made - maybe it's the overheat stat failing?)
The CH appears to cycle quicker than it should. (Possibly related to the two above issues?)

Recently though, it has developed a really annoying problem in that when the DHW is active the boiler vibrates like crazy, causing the whole house to groan as the vibration feeds through all of the central heating pipework. I've checked all of the combustion chamber panels, fan, etc. are all fitted securely and nothing obvious is loose. The vibration appears to originate from the heat exchanger but effects the CH circuit more so than the DHW. When just the CH is on there is no vibration, it only occurs when DHW is demanded. It happens if the boiler is hot, cold and with both CH on and off.

You can actually feel the vibration throughout the house by touching the radiators, it's that bad.

Does anyone have any suggestions? I'm no plumber but logic and common sense (ha ha) suggest there may be something wrong with the heat exchanger, attributing to all of the problems I have. I'm open to anything that might help!

My thoughts are that it could be bearing problems with the fan; it could maybe some weird air lock in the heat exchanger; it could be the pump failing; or it could be something more obvious that as a non plumbing engineer I've not considered!
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Its time to bite the bullet and call in local Registered gas engineer or ravenheat to diagnose and repair the boiler for you .It seems you are well out of your depth from what you have written
It does sound like a scaled up heat exchanger.

These can be descaled but its messy and not many engineers like or even know how to do it.

It should be a little cheaper as its a very expensive part. We usually charge about £180 which is probably about the price of the part itself without fitting.

We have a forum contributor called Sooey who is in your area. I dont know if he descales HEs though. We dont know for sure if thats your problem but it does sound likely.

Thanks for the response. Not sure how I seem well out of my depth but anyway... :confused:

I'd already priced the heat exchanger and was a bit startled by how expensive it is - guess that's just the way it goes!

I'll look into a replacement heat exchanger and take it from there - I'm hoping that could be the cause of the other slightly less annoying "features" of the boiler too!
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It does sound like a scaled up heat exchanger.

These can be descaled but its messy and not many engineers like or even know how to do it.


Is the descaling process a case of removing the H/E from the boiler and using a suitable chemical solution to flush the innards, maybe under pressure? After checking the cost of the H/E again (around £250) I'd like to explore other options first and if flushing is only avoided because it's messy and time consuming then I'm willing to try it first.

Reading around other posts on the forum I guess the idea is to achieve a proper deep clean in a quicker and more focussed way than just adding system cleaner to the whole CH circuit.

Thanks again.
Tony, thanks for the mention but I don't descale heat exchangers. Simply because our water up here is softer than I am, so it's not a problem I come across. Not one of my favourite boilers :LOL:
Not one of my favourite boilers :LOL:

No ***in' ****! You want to try living with one! I inherited it with the house and although it works, for certain values of the term works, it is nothing but a pain!

I'm glad you mentioned that our water isn't hard - I thought that was the case. Not convinced it actually is scale on the H/E causing the vibration but really struggling to think what else it could be.

Any thoughts?
Scale is lime scale which is calcium compounds.

Sludge is metal oxides and sometimes people ( wrongly ) use the term scale in respect of sludge.

Currently we dont know exactly what your problem is caused by.

I think that you need a competent engineer to come and diagnose your problem.

You seem rather inclined to start messing about with the heat exchanger when you dont know whats actually causing the problem.

I should also remind you that the heat exchanger should only be removed by a gas registered person as its part of the gas train.

I understand the differences between scale and sludge, and the basic underlying cause of both.

I'm just looking for some ideas as to what may be the cause of the issue, instead of just giving up and calling someone in - hence me posting the question on a DIY forum!

I'm not inclined to mess around with anything but would like to be able to do some investigation before getting a tradesmen in to save both our time.

I appreciate it is difficult to remotely diagnose problems, but was hoping for some suggestions as to what the problem could likely be caused by?
There is little point in guessing as that does not help you.

You need diagnosis, not guesswork.

A mechanical stethoscope might help you.


I've got the same boiler (it also came with the house!)m and I have exactly the same situation with the DHW temperature control. If I have it set any further then 1pm, where the black dot is printed, the it will overheat and cut-off in DHW mode. It's been like this for about five years, and not got any worse.

I'm in a very soft water area (Teesside) and my CH water looks almost as good as from the cold tap. So I don't think I have any limescale or sludge issues. One day, I'm going to put some X400 into the CH system and see if it shifts anything. But in general, I find it all works OK.

I once had an electrical fault which stopped the DHW modulating, and the other week the diverter needed replacing. Not anything out of the ordinary, going by the other posts I've seen here (for all boilers - not just Ravenheats).
my ravenheat makes the same row. on mine it's the fan. i fix my own but can't recommend that you do the same
You started ny saying your boiler is lettling. If you have correctly identified that then it would normally be a heat exchanger problem OR it could be the boiler power input is set too high.

You can check that by looking at the FAQ for "gas rate" and running hot water and checking out the gas meter. Then tell us the answer.

Another noise problem on your model csan be a pump with worn bearings.

The flow path is different on DHW from Ch so IF that was the cause then it would explain why its only a problem on one.


I "started" by listing the few on going features of the boiler - and actually asked for confirmation that what I thought was kettling, in fact was.

I then asked for some suggestions to the reason for the vibration. Logic says it would be created by some sort of mechanical action so I am guessing maybe fan on the way out, possibly pump on the way out or a simple loose fitting within the boiler. I've checked all of the boiler's components are fitted correctly as far as I can.

It only occurs if running DHW, not CH. Does anyone know if the fan runs at a different speed when DHW is in demand, compared to when just CH? If so, it could be the extra load on the fan's bearings.

Or it could be as you have suggested the bearings on the pump are failing - I've not checked yet but does the pump run when just the DHW is in demand?

I'm wondering though if a scaled or sludged up H/E could cause a mechanical vibration like I am experiencing? It no doubt is a factor in the perceived kettling and maybe possibly the limited temp control on the DHW.

At least I have a few suggestions and simple things I can test now to try and narrow down the problem.

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