Ravenheat RSF 820/20 - Intermittant cold DHW

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Renfrewshire
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Hello All!

Looking for some advice (to save me $$$)

Have recently moved to my first house with the missus and we have a Ravenheat RSF 820/20.

Central heating seems fine although these days its on constantly and its still freezing. My feeling is thats down to inadequatly sized radiators.

My problem with it is the DHW. If you put a decent demand on it, such as for a shower or running a bath, the boiler fires upto say 100%. Which is great. Water is hot and has a decent flow rate. However, after about a minute the boiler sounds as if its starting to boil and then cuts back to say 70% then the water goes cold. After another minute it goes back to full whack and the water is decent again.

It continues this same cycle until the tap is switched off.

Presure on the CH is absolutly fine although it sits around 1 bar and reaches around 2 when the system reaches temp. Whether that is bad or not I wouldnt know. As above, CH seems fine and dont have the same problem with it. Although you do hear the 'boiling' sound at times when the system has just came on from cold. i.e first thing in the morning.

Boiler has until recently been maintained by BG, and im quite sure its been maintained annually by them. From reading on the forum already, I dont beleive its the diverter valve as it has not shown the usual signs. CH flow pipe is cold when running hot water etc.

Any ideas of what to check out / possibly replace which will allow the boiler to go full whack meaning i get a fairly consisent temperature for a bath/shower unstead of this annoying hot then cold all the time?



Cheers!

David
 
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Your boiler is getting a bit old and I am surprised if BG still would take any on cover.

Your boiler has "step modulation" instead of continuous modulation.

See if you can watch the flame and see if the 100% and 70% coincide with flame size changes.

As far as I recall, its not possible to set the small flame ( at least not within the manufacturer's settings.

Try turning down the flow rate a bit and see what effect that has.

Also reduce then hot water temperature on the dial.

Tony

Tony
 
Your boiler is getting a bit old and I am surprised if BG still would take any on cover.

Your boiler has "step modulation" instead of continuous modulation.

See if you can watch the flame and see if the 100% and 70% coincide with flame size changes.

As far as I recall, its not possible to set the small flame ( at least not within the manufacturer's settings.

Try turning down the flow rate a bit and see what effect that has.

Also reduce then hot water temperature on the dial.

Tony

Tony

Hi Tony

Thanks for your responce. It has been maintained by BG since day one - they installed it.

With regard to turning down the flow rate, yes the boiler is more than happy to sit at '70%' and does not modulate. It only does it when your trying to run at full whack.

You can hear it click down and yes, you do see the size of flame reduce.

I do intend to replace the boiler but money is very tight at the moment. I'd rather get new double glazing first - that we we will get the full benefit of a new boiler.

Turning down the dial also has the same effect. It runs constantly at 70%. Unfortunatly, the flow is not enough for a 'decent' shower and takes an age to fill the bath.

Any ideas?

Cheers,
David
 
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I am not yet convinced that there is anything actually wrong with your boiler.

It may just be suffering from the very cold mains water and just unable to heat as much as you would like.

Apart from reducing the flow rate I dont think there may be anything further that you can do.

Tony
 
I am not yet convinced that there is anything actually wrong with your boiler.

It may just be suffering from the very cold mains water and just unable to heat as much as you would like.

Apart from reducing the flow rate I dont think there may be anything further that you can do.

Tony

Hi Tony

Thanks for your reply

The issue with the boiler is that it will not work at 100% for more than a minute.

Thottling back the flow rate resolves the issue however when doing so, the flow rate is totally unadequate - a bath takes an age to fill and when showering, you literally have to dance about to get wet.

Ideally, id like the boiler to maintain its maximum output for more than 1 minute. This is especially so in the mornings when you are in a rush to get to work and dont have 40 mins to spare to wait on a bath filling because the shower can only be described as crap.

I would say that its not 'broken' but there does seem to be an issue with it. From what I can appreciate, there seems to be 3 modulation steps. It will never sit and the full gas flow rate for more than 1 minute when the boiler sounds as if its starting to 'boil' and then throttles back. I could understand this if the water was 'hot' however it does only get to around 40 oC when it starts this behavoir.

Hope this helps clear things up.

Cheers,
D
 

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