Have a combi gas boiler running hot water and heating.
When I have a shower water is more then warm enough. water from the taps is hotter than I can take.
When wife takes a bath she complains it starts to run cool when bath is approx third full! I only have showers so dont know.
Assuming she is correct what are possible causes (new to combi boiler) I suggested turning on hot tap at less than full capacity so giving the water a slower flow rate hence should heat better.
Is the combi one with a small store in it (or not so small in some cases)? In this case, that may be the point where the hot store store runs out. Combis aren't great for filling baths at full flow.
What you describe is fairly normal - the incoming cold water is much colder and the boiler is struggling to cope with the flow. Yes - get her to reduce the tap opening - especially when first filling the bath.
Limited to the maximum power output of the boiler though... No standard combi is going to be able to keep pace will a half decent cold water main at this time of the year.
As indicated by the details given by the OP, his combi is not one with a built in unvented cylinder (lets face it, the *vast* majority of combis that people have fitted aren't either).
say you have a reasonably decent mains supply that can do 30 lpm, lets say its 5C, and you want to lift it to 45C, that's 40x4200x30=5MJ/min or
84kW.
What does "more than cope with" mean in your language?
Perhaps you should get in that cold bath now that your 50kW combi has taken the chill off the water.
Some have small storage vessels. Soem have integral heat banks.
A domestic gas supply can give 64kW.
No combi of 50kW can give 30 litres min flowrate at 35C temp rise. Even if your mains gives 30 litres/min when using an unvented cylinder you will not get 30 litres from the DHW tap, more like 22 litres/min.
You haven't much of a clue. Look at a 51kW ATAG with a small integral store. Rated at 25 litres/min @ 35C temp rise, that match unvented cylinders and deliver more DHW. Ethos at 54 kW. Both will cope with two bathrooms.
Indeed. Those with (i.e. a tiny minority of installed units) with integral heat banks or unvented cylinders can deliver higher flow rates for a period. Not disputing that, however I am sure you can see from the OPs post that this is not the type of boiler in question here.
(for completeness, the ones with internal small storage vessels (>>> and one that will also run on a domestic gas supply - so 50kW tops,
So, like I said not enough. Especially if sharing it with other gas appliances.
(cue some retarded nonsense about complicated interlocks to turn off your cooker every time the boiler fires...)
Even if that were the case every time (which obviously its not), your unvented cylinder will be delivering water at well above a 40C rise, and hence you bath filling will also include mixing cold. The combination of both taps will comfortably cope with 30lpm.
The wooshing sound you hear is the clue flapping past your head, dear boy. No one is denying that there are combis about that perform better than others. However that is not what was being discussed, so pratteling on about them is not helping anyone.
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