How to work an on-demand gas water heater

hi all -

i'm getting used to the concept of the durchlauferhitzer (on-demand gas water heater), but need some advice on the finer points of using it for heating, now that the weather's getting chilly - this will be my first winter in my own apartment in germany. the durchlauferhitzer system is very different (and seems more complicated) than what i'm used to back home.

there seems to be several different places one could set the temperature:
- a dial on the heater panel, for water temperature, marked 1-9
- a thermostat on the wall beside the heater marked in degrees celcius; also has a timer
- the regulators on the individual radiators in each of the rooms, marked * 1-5

first question: the regulators on the radiators, are these thermostats, or just flow controls? in other words, do they sense the temperature in the room and reduce the heat when it gets above a certain temperature? or, do they only adjust the flow, like partially opening a tap or valve?

the instructions on the heater seem to say that you should put the water temperature low (1-3) when it's not so cold out, and higher when it gets really cold. but then, it also seems to say that you should always put it high (7-9) if you have a thermostat. should i set the water temperature high (eg. 7), and then use the radiator valves in the rooms to regulate the temperature? what if i only want a little heat in one of the rooms, is that a problem?

the thermostat on the wall is beside the heater, in the bathroom. but i don't think i want the temperature of the other rooms to depend on the temperature in the bathroom. should i just ignore it, i.e. turn it up high so it never turns the heater off? what about using the timer? why do you need this central thermostat, when there are regulators on all the radiators?

i feel like kind of a dork, not knowing how to work the heat... oh well, i guess i've progressed from the first day i came, when i couldn't figure out how to flush the toilet!

thanks in advance for your advice.

If you can find the brand name and model number you can google that and maybe get a whole set of instructions with pictures. User's manual.

Thanks for asking the question - I hope someone can answer. I Googled and also contacted the manufacturer (Junkers) and haven't managed to get an instruction manual in English or German.

The basic booklet just tells you what the knobs on the boiler are, and what to do if it goes wrong - but doesn't mention the thermostat or radiator controls at all. So far we're either freezing or sweating buckets - Help!

The Durchlauferhitzer is just for heating water that you use for the kitchen and showering etc., because in some houses, there's no warm water coming from the central heating.

The heating doesn't have anything to do with the Durchlauferhitzer. You can change the temperature of each radiator using the regulator. I'm not sure, but I guess the thermostat's function is to maintain a constant temperature according to your programming in the apartment, and you can time an automatic lowering of the heating for the night. Perhaps ask a Hausmeister or the landlord how exactly it works.

- a dial on the heater panel, for water temperature, marked 1-9
This is the temperature of the hot water delivered to taps. A setting too high may end up giving you cooler water in the shower if the machine can't meet the demand

- a thermostat on the wall beside the heater marked in degrees celcius; also has a timer
This is the temperature of your house. It shouldn't be in your bathroom since that room's temperature varies drastically. This sends a sort of "overall temperature" signal to the Durchlauferhitzer to let it know when to turn on and switch off heating on the radiator line.

- the regulators on the individual radiators in each of the rooms, marked * 1-5
This is the temperature of your room. You set the individual radiator to blow as little or as much heat as you need. You may well want to save energy and kill the radiators in the bathroom, turning those on only 10 minutes before you take a shower. Likewise you can kill the bedroom and living room when you're away at work. Automatic radiator cranks with timers are available for around €100 in most DIY/hardware stores.

woof.

Central thermostats are redundant now that most radiators have thermostatic valves. Turn it up fairly high, use the radiator thermostats to regulate room temp and program the boiler to come on in the morning, off when you go to work, back on for the evening and off again when you go to bed. Sorted.

Thermostatic radiator valve.

thanks everyone for replying. a few comments:

RainyDays: "The Durchlauferhitzer is just for heating water that you use for the kitchen and showering etc., because in some houses, there's no warm water coming from the central heating. The heating doesn't have anything to do with the Durchlauferhitzer."

we have no central heating. my Durchlauferhitzer does both hot water and heating. there's a switch to select hot water only, or hot water and heating.

BadDoggie: "- a dial on the heater panel, for water temperature, marked 1-9
This is the temperature of the hot water delivered to taps."

there is a separate dial underneath, for the water temperature delivered to the taps. the dial i'm talking about sets the temperature of the water flowing through the radiators.

Wheel: "Central thermostats are redundant now that most radiators have thermostatic valves. Turn it up fairly high, use the radiator thermostats to regulate room temp and program the boiler to come on in the morning, off when you go to work, back on for the evening and off again when you go to bed."

that sounds like exactly the info i was looking for, thanks! i googled the "oventrop" valves i have, and they do indeed have a temperature sensor and theromstat operation.

by the way, i asked some of my german friends here, and they all had widely differing opinions about how it functions and how one should operate it. but Wheel's explanation makes sense to me.

OK - thanks - I see the source of our problems. The mistake is trying to save energy.

We close the living room doors during the evening, to keep warmth in. So the thermostat thinks the whole house is warm, and the radiators shut down. Come bedtime, it's still warm in the living room, but freezing in the other rooms.

So we whack the bedroom radiators up to full, and shiver in bed, b*tching about the cr*ppy heating system.

Of course we turned off the living room radiator when we went to bed, didn't we. So the living room cools down - the thermostat kicks in - and the bedroom radiators start blasting out unwanted heat (no doubt rattling & hissing) usually about three or four in the morning. Grrrr.

Maybe by-passing the one-room thermostat and buying regulators for each room is the answer. Thanks, I'll look into it.

It's important always to keep the radiator in the room with the thermostat all the way open (5). In fact, my owner's manual probably mentions that three times. Otherwise you end up with the consequence you are seeing.

Replace your thermostatic radiator valves with
Honeywell Rondostats or similar.
These give you two or three on/off periods per day
and each day of the week can be different.
You need to change the AA batteries occasionally
and programming them is a bit fiddly, but
you soon save their cost - and you always get
up to a warm kitchen or bathroom or whatever.
German Radiators are pretty standardised so
there is normally no difficulty in finding suitable
programmable thermostatic valves.