Ok to disable flow sensor?

[MDO]

Hello,

We have a tankless furnace and are happy with its performance. Other than the time it takes between switching on the hot top tap / shower and hot water arriving at the tap.

My understanding is that the furnace kicks in when its flow sensor senses water flow. The idea is to connect together the two wires that go to the flow sensor so that it always sends the signal that water is flowing even when it isn't. The furnace will turn on and heat the water inside the furnace and in the pipes near the furnace to the set point. When the output water temperature sensor reaches the set point, the furnace will switch off. With no usage of taps or shower, the standing water in the furnace and pipes will gradually cool down at which point the furnace will kick on again to maintain the standing water temperature. When a tap or shower is turned on, new cold water will flow through the furnace, the temperature sensor will sense that temperature drop and kick on again. Thus, why do we need the water flow sensor at all?

It would be just like a tanked system which is always on. In a tanked system, if I understand correctly, the water in the tank is maintained at set point always 24x7. Because the tank is well insulated, there isn't much loss of water temperature over time. I'm thinking why not do the same for a tankless system. Rather than let the standing water in the furnace and pipes get cold, just keep it hot all the time. Or at the very least, override the flow sensor at say 6am, so there is no lag when the first shower of the morning is turned on.

As well as reducing lag time, it would also save water.

Is it ok to disable the flow sensor?

If it makes a difference, we have a Bosch ProTankless GWH 635 ES N.

Many thanks,
Matt

 

[Stuff]

Very bad idea. There are probably other safety reasons but the first one that comes to mind is that something will blow up. Most systems are designed to deliver over 100,000 BTUs of heat. This is a tremendous about in a very small space all of which is supposed to be applied to moving, not standing water. The water in the coils will heat up but not uniformly and the water isn't heated where the temperature sensor is located so the sensor won't react to the heat properly . Some water will probably boil as trapped in place. In the movies you hear someone say "catastrophic failure" right before the explosion.

Note also that the damage to your house, life, and limb will not be covered by your insurance if they find out you intentionally bypassed a safety.

 

[Sponsor]

 

[Jadnashua]

The whole reason for the flow sensor is to save some energy. If you really want more instant heat, a recycling system and a tank is probably your best bet. Now, in a tankless, the thoughts above are very relevant...there is usually way more heat available than needed to flash the unmoving water to steam, and create all sorts of issues. WIth an in-boiler coil, there's usually enough protections and water volume to prevent that from happening.

There is probably a setting to raise the low-temp sensor so you'd have warmer water to start with when the flow sensor detected a demand. But, again, raising it would raise the standby losses, and cost money.

 

[DonL]

The idea is to connect together the two wires that go to the flow sensor so that it always sends the signal that water is flowing even when it isn't.

That sensor most likely puts out a pulsed signal. I do not think that would work, and a safety will most likely shut it down.

As mentioned, It is a bad idea.

Why not just install a heater with a tank ? A Tankless will never work as good as old school.

Good Luck.