Winter only issue with tankless

[bearcalypse]

Item: Bosch Aquastar MODEL 125B NG
Location: New England
This thing must have been in the house for a while when we bought it and in the summers it works like a champ and we get limitless water for showers, jacuzzi, all the sinks.

In the winter, late fall, early spring - it just can't heat the water in the shower sufficiently **unless** I have a faucet running a trickle from the HOT lever somewhere else (bathroom/kitchen sink) at the same time. On alone, the water isn't ice cold like it would be from the cold setting - it's definitely warmer than ambient, but not actually hot until some other faucet is turned onto HOT.

I've had plumbers over and all of them quote me over 10k to replace it with a newer model but the newer ones offered are power vented and need an electrical hookup to even work - so if I replace this, it'll be with a tank because I am not in a position to be also paying for an electrician to be running a whole new electric supply to this location. I ask the plumbers - hey if it's dying and can't heat the water when only the shower is turned on, then why does it heat the water just fine when the shower and a faucet is pulling hot water? Shouldn't increased hot water flow make the water less hot since it spends less time in the heating coils? All I've got is stammers that old models have poor flow control and there is no way to regulate it.

So if it's a matter of regulating it, couldn't I just run a 1/4 or 1/8 inch diversion from the hot water output back to the cold water input with a backflow preventer to just make it recirculate some of that heat better and save on a super expensive replacement?

Thoughts, ideas, solutions - all appreciated.

Thank you.

 

[GReynolds929]

Has the flow sensor been checked?

 

[Sponsor]

 

[bearcalypse]

Has the flow sensor been checked?

Thank you for the lead.
They have checked the water valve - which I am guessing is where the flow sensor is? The first company I had over replaced the plunger/nipple piece in there which the manual says is the pushrod. That did not change the way it performed.

 

[GReynolds929]

Was the valve adjusted/calibrated when it was replaced? It's been a while but IIRC the plunger gets screwed in until the ignitor starts clicking and then back it of a certain amount. Not sure if this helps.

 

[Fitter30]

Your heater is only 117k input. Measure your coldest incoming water, max gpm flow. Then look at anyones condensing heater in sure your short of capacity.

 

[Jeff H Young]

too small a unit shouldnt require the shower and a sink to be on to get hot water it would worsten the situation no way thats the issue something else is going on? maybe its the shower valve ballance spool

 

[royalflush001]

Introducing a recirculation loop involves redirecting hot water back to the cold water input. This could potentially create a situation where hot water is unintentionally introduced into the cold water supply, posing a safety risk. A backflow preventer is a good idea, but it's important to ensure that it meets plumbing code requirements and effectively prevents cross-contamination.