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hot water too hot.

Postby rustyriv » Mon Dec 27, 2010 11:22 am

Hello folks, I have a conventional y plan open central heating system, I recently replaced an old condensing energysaver boiler with a worcester 24ri greenstar, the energysaver required a by-pass across the coil in the cylinder the worcester does not so this was closed my problem is whenever I turn the new boiler temp. up beyond the middle position, the water out of the taps is in the region of 70 degrees 'c' I bought an infra red temp. sensor, to measure the temp. on the outside of the cylinder when I take off the cyl. stat to measure the temp behind it, it is only some 30 'c', about the same temp. as the outgoing pipe on the top of the cylinder but the water temp. coming out of the taps is 70 'c' ! how can this be? turning the cyl. stat down to 50 'c' does not seem to achieve anything but then it would'nt would it! the recovery rate is certainly very good now I guess about 15 mins.can it be that the coils in the cylinder are so efficient that the temp. in the top of the cylinder is way above that of the temp. 2/3rds of the way down where the stat is, or could it be that there is a build up of calcium in the bottom of the cylinder preventing the actual temp of the water being transmitted to the cylinder wall?
I am at a loss, I would like to run the boiler at as hot a temp. as possible in this current weather for efficiency purposes but the water temp. is hot enough to burn you, should i entertain the possibility of opening the by-pass again?
I have always used a water treatment device which is hung in the cold water tank, does anyone have any feedback about these? so I woud'nt like to think there was excessive calcium build up. does anyone have any ideas? regards,
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Simply Build It

Postby cotswolds » Wed Dec 29, 2010 2:06 pm

Infra red thermometers aren't quite as simple as they seem.They have to make an assumption about what you are pointing them at, and work very badly for reflective materials (which your copper cyinder is, even if it doesn't look very shiny). They are most accurate with matt black surfaces, but are OK for most non reflective surfaces. Try taping a piece of dark coloured insulating tape on to your cylinder (and the pipe at the top) and pointing your thermometer at that. I'd be surprised if you don't get something close to 70.

I've just been balancing my CH system and couldn't understand why the hot flow out of the boiler was 30 C - sticking a bit of tape on gives the expected 60 C. The colour of what you use is less important than it being in good thermal contact with what you are measuring.

Your cylinder stat should do what you want, but remember you'll have to run off the 70 C water before you can take another measurement, it will take quite a while to cool to 50 C if it's not being used.

Incidentally, condensing boilers are most efficient when run as cool as possible. It's sensible to turn the temperature up in very cold weather (if there isn't an external sensor) but only enough to keep the house warm, and turn it back down when the weather warms up.
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