Boiler firing on hot water but water only luke warm.The temp gauge shows 60c.Corgi installer but not very experienced on combi faults,guess its DHW thermistor or Heat ex but would like a experienced opinion.
Biasi Garda HE combi
- Thread starter tony73
- Start date
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Have you measured the DHW flow rate and the temperature rise to see exactly how the boiler is performing compared with the spec?
When you have set it to the design flowrate measure the differential temp across the plate HE. It should only be about 15-20°C. If much higher suspect a blocked plate HE or just possibly a lime scaled secondary but thats unusual unless a tap has been dripping.
If the defect has not become clear by this point then measure the working pressure at the boiler and the burner pressure at max and min.
Its most unlikely to be anything to do with thermistors!
Tony Glazier
When you have set it to the design flowrate measure the differential temp across the plate HE. It should only be about 15-20°C. If much higher suspect a blocked plate HE or just possibly a lime scaled secondary but thats unusual unless a tap has been dripping.
If the defect has not become clear by this point then measure the working pressure at the boiler and the burner pressure at max and min.
Its most unlikely to be anything to do with thermistors!
Tony Glazier
Could you tell us;
How long the boiler has been in,
Was it put in at the same time as the Radiators,
Was it put in to replace a boiler and hot water cylinder arrangement, if so was the gas pipe increased in size to a 22mm pipe?
Thanks,
Tim
PS If you are not experienced at working with gas I suggest you dont do this bit your self,
Er... he has said that he is CORGI registered Tim!
I would never suggest that anyone checks gas pressures unless he is registered.
Tony
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Tony you appear to be unable to note the nu·ance of my PS, it is a subtle Gas Safety Message to those viewing this site seeking advice. (a, was it to subtle for you, emoticon)
Tim
I also subtly did not mention "gas" in my suggestion knowing that many DIYers would not follow what I was saying!
I always like to keep my gas safety messages clear and bold!
"Dont mess with gas unless you are CORGI registered ( and preferably a member of ARGI as well! )"
Tony
I always like to keep my gas safety messages clear and bold!
"Dont mess with gas unless you are CORGI registered ( and preferably a member of ARGI as well! )"
Tony
Sorry tony73 I did not ask the obvious question, what flow rate in litres per minute that you get at the hot tap in the kitchen sink?
I ask because I have just returned from a terraced house in which I was filling a three gallon bucket.
The bucket filled in double quick time!
That was something like 18 litres a minute, no Guarders can cope with that flow rate.
It would be good if an inexpensive answer to your problem was just to reduce the flow rate to one which the boiler can cope with, is it the 24 or the 28?
Tim
I ask because I have just returned from a terraced house in which I was filling a three gallon bucket.
The bucket filled in double quick time!
That was something like 18 litres a minute, no Guarders can cope with that flow rate.
It would be good if an inexpensive answer to your problem was just to reduce the flow rate to one which the boiler can cope with, is it the 24 or the 28?
Tim
Wouldn't it have been more polite to ask the customer if you could have used the toilet Tim
Have had a look at my MI of the M96 and it would appear that the central heating temperature probe is in the pipe flowing from the primary heat exchangers.
Thinking about it if the DHW temperature knob is on max then If we are trying to get water at the hot tap to reach 55 degrees centigrade then surely it should be leaving the primary heat exchangers at some thing like 75 degrees to enable a high enough temperature through the primary side of the plate heat exchanger.
Other wise there will not be enough heat energy to raise the temperature of the DHW side of the plate heat exchanger.
So is we have water flow rate all right, and is the hot water knob turned fully on, and the boiler was working alright before, is the plate heat exchanges still the likely culprit?
Tim
Thinking about it if the DHW temperature knob is on max then If we are trying to get water at the hot tap to reach 55 degrees centigrade then surely it should be leaving the primary heat exchangers at some thing like 75 degrees to enable a high enough temperature through the primary side of the plate heat exchanger.
Other wise there will not be enough heat energy to raise the temperature of the DHW side of the plate heat exchanger.
So is we have water flow rate all right, and is the hot water knob turned fully on, and the boiler was working alright before, is the plate heat exchanges still the likely culprit?
Tim
the problem is that the devil is in the detail and there is not much of it!!
we need to know
the power of the combi and the flow rate as tim righty pointed out
but also check that internal by-pass is not stuck open
they dont make a 32kw Garda HE combi
Sorry, yes you are quite right!
They made a 32kW M90 but for some reason never made a 32 kW M96.
Tony
Thanks for the advice fellows,the boiler is a 28 and the gas is run in 22mm.
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