Been having a problem with my ravenheat 820 for quite a while now, changed the diaphragm a while ago as couldnt get dhw without heating on so thats not the problem. Problem is the burner doesnt seem to modulate correctly, seems to be more of a problem with the shower , turn on shower water gets hot, get in shower and after a couple of minutes the water goes cold, stays cold for a minute or so then gets hot again. The burner switches off when it reaches stat temp instead of stepping down to low burn, it sometimes switches to low burn but then switches off after a few more minutes, its almost a if the boiler is overheating and turning itself off. Flow rate is good and is set as it has been for the last 7 yrs. My mates a plumber and suggested that the dhw temp sensor might be duff. Can anyone confirm this before I start buying parts
Ravenheat 820 hot water cuts out
- Thread starter fallwood
- Start date
check thermostat hasnt gone on shower first
Already changed it. Its a gainsborough that uses the aqualise pink combi cartridge. Hot water doesnt seem to go off when i open a tap but i suspect thats because it never gets up to temp as the flow rate is set quite high, i have to turn taps down to get really hot water but i like it like that as i can fill a bath from the hot tap and get straight in. Boiler worked ok for 1st 5 yrs then seems to have got worse over past 2 yrs to the point that i cant use the shower as it wont keep hot for more than a minute at a time.
Its a likely cheap thing to start off with!
I'd be suspecting a pump on its way out. Is it noisy?
Investigate a probable slow flow of system water through your heat exchanger.
Pump seems to be fine (very quiet) , do you mean flow of ch water through heat exchanger, the problem seems to be whatever controls the step modulation of the boiler, sometimes it steps down to low burn but most of the time it just cuts the burner, if i slowly turn down the dhw stat till it clicks off, the gas solenoid clicks to step down the burner but most of the time it cuts the burner immediately, it used to just step down to low burn and then if i turned stat back up it would kick back in to high burn.
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Under normal usage when its working correctly, under what circumstances would the burner cut off completely when using dhw, when water reaches stat temp it should step down to low burn shouldnt it , not turn off completely.
MOD
please see 10a
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Under normal usage when its working correctly, under what circumstances would the burner cut off completely when using dhw, when water reaches stat temp it should step down to low burn shouldnt it , not turn off completely.
MOD
please see 10a
If the temperature at the sensor is too high by sufficient margin, it will cut the flames, This could happen due to a faulty sensor, flow being too slow to remove the heat fast enough, or insulation of the sensor or heat exchanger(s) due to sludge.
Slow flow is caused by a pump going slow or being sludged up, or the h/e(s) or waterways being sludged, or a flow limiter fallen apart.
I have been fooled by a pump seeming to be ok when it wasn't.
Slow flow is caused by a pump going slow or being sludged up, or the h/e(s) or waterways being sludged, or a flow limiter fallen apart.
I have been fooled by a pump seeming to be ok when it wasn't.
I recently came across a similar situation with a combi boiler and new thermostatic shower. I think this sort of problem may arise at this time of year because ambient temperatures (including that of incoming mains cold water) are relatively high. This has 3 consequences.
1. Lower shower temperatures are selected by users during warm weather.
2. Cold water mixing in shower is warmer, so less hot is required.
3. Cold water entering combi is warmer, so requires less heat.
Consequently the amount of heat input required of the combi can be towards the bottom end of the modulated range. Therefore total shut down of flames by a stat may occur, giving rise to alternating hot and cold water supply.
I checked the low flame burner pressure setting against manufacturer's data (not Ravenheat in this case) and found it was 3 mb rather than 2 mb. I reduced it to 1.5 mb and this solved the problem. Please note that altering burner pressures is strictly Corgi reg. territory.
1. Lower shower temperatures are selected by users during warm weather.
2. Cold water mixing in shower is warmer, so less hot is required.
3. Cold water entering combi is warmer, so requires less heat.
Consequently the amount of heat input required of the combi can be towards the bottom end of the modulated range. Therefore total shut down of flames by a stat may occur, giving rise to alternating hot and cold water supply.
I checked the low flame burner pressure setting against manufacturer's data (not Ravenheat in this case) and found it was 3 mb rather than 2 mb. I reduced it to 1.5 mb and this solved the problem. Please note that altering burner pressures is strictly Corgi reg. territory.
So far ive changed the thermocouple cut off thermostat and the high limit thermostat and its still doing it, i suppose the pump is the next logical step, dont really want to fork out for a new pump if it turns out to be the heat exchanger thats clogged up/warped/knackered, if heat exchanger gone i may as well buy a new boiler as its almost half the price of a new one. Do ravenheat have their own service team that carry spares so they can try a pump to see if its the problem.
Fallwood - a boiler engineer would find out what's goin on by measuring thr temperatures round the circuit, how they go from cold and during use. Different chaps uae different methods - I could check the rpm of the pump for example.
ChrisH - the other exacerbating factor can be the behaviour of the thermostatic mixer itself. If shower water is a bit too hot it reduces the flow of the hot a bit. But it's a combi so the water coming from it gets hotter, so the valve cuts it... etc... until the boiler overheats and turns off.
ChrisH - the other exacerbating factor can be the behaviour of the thermostatic mixer itself. If shower water is a bit too hot it reduces the flow of the hot a bit. But it's a combi so the water coming from it gets hotter, so the valve cuts it... etc... until the boiler overheats and turns off.
low gas pressure is set at 1.5mbar high is around 8.1mbar. Seems to be taking its time firing up the burner when I open the tap now, im sure it used to be instant. Wonder if the diaphragm has gone again (only been in about 8 months). To be honest ive just about had enough of it and am considering picking up a new boiler tomorrow, just cant be arsed messing about with it any more.
Sorry , didnt realise a****d was considered bad language, what make and model would you reccomend I go for as the 820 has never worked very well with my thermostatic shower mixer, am I right in saying I need a fully modulating boiler and not a step modulated one if I want the shower to work correctly.
Not necessarily, they just odcillate more smoothly!
Lots of boilers eg Vaillants have never been fully modulating on HW, but they go hi-lo so quick you don't notice, if everything is tickety boo.
I don't know about the Ecotecs..
Just thought id let you all know my boiler s now fixed. Had a local boiler engineer come have a look at it and he fixed it in about 10 mins, apparently the pipes that lead from the fan to the air pressure sensor were clogged up with fluff and dust causing it to cut out, gave it a good blow out with the compressor and all is well. Another point well made in favour of regular services.
ChrisR said:
All I know is thats what the engineer told me, as far as i could see (i like to stand and watch) he removed the fan took it outside gave it a good blow out with a mini compressor and then re-fitted it, its been running fine ever since, apparently its a very common problem on the 820 and he made a bee line for it straight away.
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