Hot water / low flow rate or tepid water, high flow rate

8 Feb 2010
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United Kingdom
For two years I've had a shower over my bath that had a very high flow rate and always produced hot water.

During the recent snows my boiler, for the first time returned an error of two flashing red lights, an error indicating "no flame detection".

I let the boiler cool down and reset it, and relit the flame. That started the central heating to come on, and my radiators get plenty hot enough.

What hasn't been right since is my hot water. At high flow rates it no longer gets really hot. Sometimes even with a dribble the temperature isn't particularly warm (approximately 25'c). A gascare plumber has looked at the boiler and pronounced it ok and recently came again to look at the hot water issue.

The solution, to get hot water (40'c), was to reduce the flow rate through the boiler. That's now got me hot water, but not at the same pressure as before - roughly half as much.

Is it because of the colder weather and water temperatures? What could I do to get the same pressure at the high temperatures back? Basically I'd like to understand what I can do to get the high pressure AND hot water I enjoyed before. A bit greedy but something has changed. I'd like to understand what.

The boiler is a Chaffoteaux and Maury Britony Combi SE.

Many thanks in advance.
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Whats the boilers output , this will be expressed in either B.T.U's or K.W ??
Hullo, for the 80 DHW Gross is (kW) 28.7, in BTU/h 98000.

At this precise moment the boiler is showing the same error as before, "No flame detected".

The plumber today checked my gas input and declared it perfectly healthy! Should I be calling the supplier to check warranty?
If your boiler has an output of 28k.w than , it should produce a a 35 deg temp rise at a flow rate of approx 11.5 litres a minute . A temp'rise means that the boiler will increase (raise) the temp' of the incoming water main by 35 degs C at that flow rate , e.g IF the temp' of the water coming into your prop' is 10 deg's than 10 +35 = 45 degs at a flowrate of 11.5 litres a min , if your incoming water is 5 degs C than 5+35= 40 degs C at a flow rate of 11.5 litres a min , so & so forth , all flowrates from most combis will quote the term delta or make ref' to it with a small triangle which is math's symbol for Delta , meaning the increment of a variable , the variable in this case is the temp of your incoming water main . You can apply other temp' of hot water & flowrates I can give U the formula if U like . U can check the performance of your boiler with a thermometer and awater measuring jug . if the gas rate & pressure is correct , any temp sensors are correct than a scaled up heat exc ' if boiler is going to lock out call them back !!
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Apologies - I'm having a bit of difficulty here - could the "no flame detected" and high flow rate - but low water temperature - be related to a heat exchanger not working efficiently? As in, it has significant water scaling? Is there a way to check this?

The delta equation was handy. I'm assuming that due to the cold weather the water is also cold, thus the maximum temperature coming out being about 40'c.

Would a scaled heat exchanger also be the root cause of this no flame detected error, i.e. the gas flames going out and needing to be relit frequently?
Could be if the boiler is over heating , & the boiler is locking out on high limit , ?????
U can apply other tempuratures the 35 deg C is ind' standard , in order to do so u convert the out put of your boiler into Kilo calories 1 k.w =14.3 k.c 28 x 14.3 = 364 divide by your wanted H.W temp say 50 = 7.28 there fore the combi will produce approx 7.28 litres a min at 50 deg' C , so on & so forth , use other temps , these types of check would indicate a scaled up heat exc' . your rgi having checked the gas rates & pressure's ect , & u still had a prob ' should make this type of check ???

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