Hot bath water

[lobsters15]

We have a 30 year old Baxi Bermuda fire with a back boiler and although I know it is inefficient it provides us with plenty of hot water. I am told by Scottish gas engineers with whom we have a maintenance contract that spares for this fire will be soon unavailable.
At present the water in our hot water cylinder gets up to 82°C and this allows my wife to take the long hot baths she enjoys ( bath water at 46°C)

I have had many heating engineers to the house so they could advise on a new boiler and I am thoroughly confused. Am I correct in thinking that no Combi boiler could provide a 46°C bath in a Scottish winter where incoming water can have a temperature of 4°C. I am told that Combis can only raise the temperature by 35°C.
I have considered a system boiler but have been told that regulations state that the thermostat on the hot water cylinder can be adjusted to no higher than 60°C resulting in a bath with a lot less water at 46°C.

 

[Agile]

Your hot water is being stored at too high a temperature.

I dont understand anyone who wants to run their system in an inefficient way.

There is no need to add cold water to a bath. Nor do I think your wife can stand a bath at 46°C.

A combi boiler can produce water at up to about 50°C. They are just specified as the flow rate to be raised by 35°C.

If your back boiler is the 552 then they are lots fitted and spares are likely to be available for at least 10 years. BG try to frighten people into getting them to fit replacement boilers.

You dont need a combi either! You can have a ( cheaper ) heat only boiler fitted to retain the existing or a replacement cylinder.

Tony

 

[lobsters15]

I do assure you that my wife has a bath at 46°C and I do no want to replace our system with one which delivers lukewarm baths in winter time.
You mention that Combis can deliver water at up to 50°C but could they do this in a Scottish winter with an incoming main's temperature of 4°C.

 

[pgod3]

a combi could heat your hot water fine but as said above the boilers flow rate is given at a 35 degree rise. heating the water to 50-60 could drop the flow rate of the boiler.

Have you considered installing a combi boiler with the instant hot water being used for your kitchen and then installing a small unvented cylinder for hot water to bathrooms. This would mean you dont need to raise the combi boiler temp too high with no drop in flow rate and all you would need to do is split the flow and return to a S plan for heating and hot water. i have done this for customers and have been successful

 

[lobsters15]

Many thanks for your help. What I am trying to find out with great difficulty is a water flow rate/ temperature table for any boiler. I was thinking of a 40kW baxi combi because it had a flow rate of 16l/min.

Am I correct in thinking that the 35°C increase in temperature assumes maximum flow rate? If I reduced the flow rate to 10l/min what would be the temperature rise in the Baxi mentioned above be? I contacted technical support at Baxi but they really could not provide an answer other than it would be hotter. They suggested forget the combi and go for a Megaflow. However if there is a 60°C ceiling on hot water in the cylinder deep hot baths, as we get just now, will not be possible.

 

[pgod3]

there is no ceiling as such with hot water it is advised though to store your hot water at around 60-65. this is because any hotter you are starting to create more scale especially if your in a hard water area. most boilers flow rates are given with a increase of 35 degrees. i personally wouldnt know off hand the temp/flow rate chart you are after. Personally i think an unvented cylinder aswell as the boiler (which ever boiler you choose) is a good idea if you want a balance of good flow with temperature

 

[IKJ]

If you have to heat your water that high to get a bath full of water its because your tank is mostly full of scale

 

[lobsters15]

The hot water cylinder is new and the water is very soft living in Glasgow and receiving almost solute free water from Loch Katrine.

 

[bengasman]

...You mention that Combis can deliver water at up to 50°C but could they do this in a Scottish winter with an incoming main's temperature of 4°C.

No problemo. Provided the combi is big enough, you will be able to get unlimited piping hot water even during prolonged spell of extreme cold. It will take just a little bit longer at that point.
If you do go that way, I'd recommend a Worcester Bosch 42 CDI; very good hot water production and a much better boiler than the baxi.

If your boiler is currently working to your satisfaction, keep it. There is no shortage of parts at the moment and it won't change overnight. When the spares get rarer, it will be at least a full year, probably longer before they change from a bit harder to get , to impossible to get. Somebody is just trying to line up work.

 

[lobsters15]

I contacted the technical department at Worcester Bosch about the Worcester Bosch 42 CDI combi boiler regarding temperature. They told me that this boiler would raise the water by 40C. I asked could I get temperatures that were much higher than 40 degrees C by reducing the flow rate. They told me that it would be a bit hotter but could give me no information as to how hot it could go. Surely this should be easy to find out, a simple flow rate/temperature graph.

 

[glasgowgas]

ok here goes.......

a 24 kw combi will give a 35deg temp rise at 9 litres per min

incoming water = 15 deg
bath flow rate = 9 litres per min
bath = 60 litres

filled bath with 50 deg water in less than 7 mins

incoming water = 8 deg
bath flow rate = 5 litres per min
bath = 60 litres

filled bath with 50 deg water in 12 mins

so at recommended flow rate water will give a 35 deg rise

reduce flow rate = increased water temp = longer time to fill bath


go with bens advice

 

[lobsters15]

Thanks for the info. So if I went for a Worcester Bosch 42 CDI with a flow rate of 15l/min I should be able to fill a bath fairly quickly in winter time with water at about 50 degrees C?

I assume the flow rate is controlled at the bath tap rather than adjusting any boiler control.

 

[glasgowgas]

I assume the flow rate is controlled at the bath tap rather than adjusting any boiler control.

the boiler should be set up so that the maximum flow rate is going through it

once that is done turning the bath tap down, would give a higher temp/lower flow rate

 

[bengasman]

...They told me that it would be a bit hotter but could give me no information as to how hot it could go. Surely this should be easy to find out, a simple flow rate/temperature graph.

2 options:
1. You spoke to 16 year old blonde who didn't know that much
2. You spoke to somebody who was just being polite; answering that sort of questions is the job of your supplier, not the importer.

 

[bengasman]

Thanks for the info. So if I went for a Worcester Bosch 42 CDI with a flow rate of 15l/min I should be able to fill a bath fairly quickly in winter time with water at about 50 degrees C?

Any boiler has a certain power: let's call it P.

Time to fill the bath = (volume of bath x (required temperature - incoming temperature))/ P