Something for Nothing

[WoodlandsCamper]

Our gas fired central heating boiler has been playing up over the last few days, so the man in a blue van came to look at it. He was trying to treat the OH as a dumb woman by saying that if the boiler thermostat was turned down to 40 degrees we could still have water out of the taps at 60 degrees!!! This was in response to the OH saying that tap water had to be above a certain temp to combat legionnaire's disease. Please could one of the professors on this forum explain how this free 20 degree increase can happen (other than blue van man saying 'residual heat').
Should blue van man be called an 'engineer' or 'gas fitter' or something else?

 

[Sproket]

I ain't no professor

But..............

We have a condensating boiler that has its own separate thermostat for the water temp & own for the central heating.
Radiators can all be on low & when the taps are turned on the water is as hot as you care to have it.....
http://www.nef.org.uk/energysaving/boilers.htm

 

[WoodlandsCamper]

Our boiler is also a condensing one, but it only has one output pipe which goes to a pump. After the pump the pipe splits into two branches, one to the indirect coil for the hot water cylinder and the other to the central heating. Both branches have their own motorised control valve (to shut down that branch) driven by a themostat giving the same effect as you have. However I would have thought neither branch can get any hotter than the water coming out of the boiler, which blue van man said it could.

 

[Sproket]

Sir WC

This is what it says in the manual for our boiler:
http://www.ravenheat.co.uk/pdf/guides/CSIUSER_SGUIDE.pdf

OPERATING DOMESTIC HOT WATER
2.0 Select only switch position (1).
2.1 Open hot water tap.
After about 3 seconds burner will always operate.
2.2 Temperature of domestic hot water can be varied by adjusting the water flow rate at the tap.
Domestic thermostat (5) will control maximum temperature leaving the appliance.
The knob can be set between minimum and maximum approximately 35 °C to 65 °C (95F to 1 49F).
For maximum temperature of domestic hot water leave in maximum position.
3. OPERATING HEATING & HOT WATER
TO SET AND ADJUST BUILT-IN TIMER MODEL SEE OPPOSITE PAGE 3.
3.0 Select switch (2) position.
3.1 Switch on time clock, adjust room stat and/or thermostatic radiator valves to high settings.
3.2 Burner will operate. Temperature output of
central heating can be adjusted by central
heating thermostat (4).
The knob can be set between minimum and
maximum approximately 40 °C to 85 °C (1 40F to 1 85F).
While the appliance is being used to provide domestic hot water, the central heating will not operate.
When hot water is no longer required the
appliance will automatically revert to central heating and should not noticeably affect the level of central heating.

Have a look on this link to Boiler-Manuals to find your type / model to clarify things

 

[Damian]

It depends on what kind of system you have.
I believe Woodlands Camper may have a hot water storage tank whereas Sproket does not.
From Sproket's description his is a multipoint boiler which supplies hot water on demand from the tap whereas a storage system has a readily available 40 gallon or so hot water tank, usually in the airing cupboard .
Each system , at least modern systems, have different controls for domestic water and central heating.
The hot water storage system has a temp stat on the tank to control the heat of the hot water, and either a room stat or radiator stats, or both to control the central heating.
However, the main boiler stat dictates what temp the boiler will reach and if that is set to 40 degrees, that is the most you wil get out of it.

The optimum setting for the boiler is 80 degrees which allows fast heat up and recovery for a tank system.

 

[colin-yorkshire1]

ah, Damian beat me to it I was going to say the very same thing, different sytems spring to mind,

WC, has the same set up as we have, IMO the engineer is talking out of his exaust pipe,
The internal thermostat of the boiler sets the water temp comming out of the boiler to the pump, this is the hottest it can be if it's set at 40 degrees thats all you get.

 

[WoodlandsCamper]

Thank you all for your replies. Yes Sir Chunky, you agree with me, in our type of system you can't get any higher than what the boiler thermostat is set to.

 

[DeliDave_]

Damian has given an excellent explanation and to add to that ,having the boiler at 40 and cylinder at 60 will mean the pump is running whenever the timer is calling for heat as it can never satisfy the thermostat so you will be wasting energy and money and adding to wear and tear on the system.

 

[colin-yorkshire1]

Damian has given an excellent explanation and to add to that ,having the boiler at 40 and cylinder at 60 will mean the pump is running whenever the timer is calling for heat as it can never satisfy the thermostat so you will be wasting energy and money and adding to wear and tear on the system.

sorry "Sir Deli Dave" thats not right, in the system we an "Sir WC" have there is no way to set the cylinder temp seperatly, because the hot water cylinder is heated by the induction coil in the tank that is piped direct from the boiler, the central heating does not have a seperate tank but is also piped direct to the radiators from the boiler, all the water in the outwards flow of the system is the same temp, because it is the same water!! all one can do is set the priority h/w and/or c/h, while the temperature of the c/heating can be altered by the wall thermostat, "upto the same temp as the water" the "hot water" cannot be altered exept by adjusting the boiler thermostat.
now there are two problems with your suggestion, (1). is once the central heating or hot water is switched on the pump constantly runs it does not shut off only the boiler burner shuts off, water is pumped through the system all the time until it cools down to a point where the boiler thermostat relights the burner there is no extra wear or tear as that is how the system was designed to work
and (2). given that hot water @80 degrees can be used to make coffee and is hot enough to scald why would one want it that hot!! it is too hot for the washer (40degrees) and too hot for washing anything without using as much cold water as hot, and seeing as how most room temperatures are set below 30degrees, 40 or 50 would be fine.
one last point, the boiler when it is first fired up will take far less time and energy to get up to temp @40 degrees than it would to 80 and will cut in and out less often when it is up to temp. this will cost a lot less to run overall not more.

 

[DeliDave_]

Havent you got a thermostat on the hot water cylinder then

 

[Damian]

Quote " 40 or 50 would be fine."

No it would not.

Hot water must be heated to a minimum of 60 degrees to prevent Legionaires Disease.

Ideally at least 70 degrees, which is why Truma have the electric heating factory set to 70 degrees

 

[colin-yorkshire1]

Havent you got a thermostat on the hot water cylinder then

NO, only on the electcric emmerson heater

 

[colin-yorkshire1]

Quote " 40 or 50 would be fine."

No it would not.

Hot water must be heated to a minimum of 60 degrees to prevent Legionaires Disease.

Ideally at least 70 degrees, which is why Truma have the electric heating factory set to 70 degrees

thanks for that, I was not aware that the UK mains water contained Legionaires Disease. as it is treated with Chlorine.
and outbreaks (rare) are usually traced to rooftop holding tanks (not treated) that are used for heating and air conditioning,

no part of the boiler heated water can cross contaminate the drinking water as it is a closed system, unlike a caravan or instant heat system that does, I allways assumed that the higher temp used on vans was because some people use there vans abroad and truma have no idea which these will be, so pre set the temp accordingly to kill of the bugs in untreated water supplies.