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In this week's video, I talk about how to electrically troubleshoot a friday afternoon no heat boiler call without an electrical diagram.

old one is but it is being replaced with a conventional ci boiler because of reliability issues with that particular combi.

It's hard to beat the simplicity of a thermostatic return valve. Thermostatic bypass valves have been used in various boilers for many years. Most pool boilers have them built inside. The weil GV gold CI boiler had one built in.

With the large pipe, low head loss system you have a single pump would probably do the job. Check the boilers recommendation for pump.

The color schematic below happens to show the buffer as the load, same concept. Step 2, allowing a portion of the return to blend in may happen in minutes, it may take 1/2 hour, it is all based on the load and boilers delivered output. if the boiler is oversized to the attached radiation, the most common match, then the valve opens faster.

The largest market for these valves is the wood boiler industry. I spotted a handful of manufacturers with these valves at the Mostra show in Italy a few weeks back. So they talk more about solid fuel problems, like creasote formation same physics at work with fossil fueled boilers.

A pump and controller plus flange set. A bit more $$.

I think the VS pump like this color drawing makes sense. This piping concept has been used for years with CI boilers connected to low temperature radiant as it both mixes and protects the boiler, basically called "injection mixing" It's the concept and product that put tekmar on the map

The Taco schematic below this schematic, see the difference??

It's all about the pump placement. Again how does the pump "speed up" to overcome the large thermal load? It's not adding any heat energy. Only if the distribution pump drops off could that happen, the thermal clutch would be the boiler pump. may as well just use a $50 aquastat to hold the pump off.

The ONLY reason to use any return protection method is the load /distribution is much larger that the boiler can keep up with, suppressing it's operating temperature condition. May as well pipe and control it with a appropriate fix as the goal, not a "maybe" That was the whole point of injection mixing!

I'm not sure how this US Boiler solution works without a system pump?? They show system pumps on the other methods? A bit misleading for the inexperienced installer.

If you put some typical numbers to a system you will see the issue.

Assume a cold start boiler, not a tankless coil boiler?

On call for heat water returns at room temperature, or cooler depending on piping location.

So assume 68° is coming back from a 180 gallon high mass radiators, large steel pipe.

the boiler is sized close to the load and radiators connected expect at a design condition the boiler can "lift" the temperature a few degrees, call it 72°.

How does a variable speed pump increase the temperature to get the boiler to 130?

The only possibility would be to turn off the system pump to allow the boiler to catch up to120- 130. If so why have a bypass pump? Just bang bang the system pump on/off based on return temperature, saves an expensive pump.

A proper return method has a means to disconnect the load from the boiler, based on a temperature reading.

This is why a bypass valve or pump is only a guess and works at the condition you set it up at. When is that? Coldest day, full load on the system? Boiler hot or just starting? What happens on a low load, medium load condition? Too much bypass?

We talk about a "thermal clutch" a means to allow the flows to modulate at the exact rate the boiler can accomodate.

This is what a 3 way mix valve does, or a properly piped VS pump.

With a low head system, a single circ can work.

With multiple zone pumped systems, or high pressure drop distribution, closely spaced tees with a mix valve. Zone an boiler pump sized accordingly as you have hydraulic separation in this option.

The small piping change in this next drawing allows the load to disconnect from the boiler. The VS pump, as a P/S close tee piping, injects energy into the system based on a return sensing, a motorized thermal clutch solution. With this solution all 3 pumps could, should be sized to their exact loads. The boiler pump as per the manufacturers spec choices. The injection pump, based on the injection formula, ususlly a very small circ.

The distribution pump may be a high flow low head version on a gravity conversion, could be a medium or high head on a radiant tube system.Thrin

Explanation below

This is a lot like the Pumping Away concept and discussions. Plenty of installers claim pumping away is a waste of time, not needed, ,pumping into boilers and expansion tanks has worked fine for generations, why else would boiler manufacturers put pumps on boiler returns?

When you say the "variable speed bypass method" are you referring to exactly how the US Boiler bypass kit works? Why can't it offer 100% protection? I'm not questioning your knowledge, I'm just genuinely trying to understand this for myself.

If I think this through on my own a bit, your answer is probably going to be that the pump can only ever take some capped % of the total GPM leaving the boiler. But the pump can never redirect 100% of the total GPM leaving the boiler back to the return. Whereas a 3-way valve (mixing valve?) will not allow any flow to leave until it hits the setpoint temp… NOW WE'RE GETTING SOMEWHERE.

So if I'm picking up what you're putting down - the preferred method here is to use a single 3-way valve? Is there a Heating Help concensus on that?

If I were to have this contractor just install it without a bypass piped in, would you guys say it's within the capability of a homeowner (me) to install a 3-way valve after the fact? My wife is really getting fed up with me "overthinking" this replacement, so I (she) was really hoping this company would be the last one… 😁😅

Just to prevent condensation issues in the flue (as far as I know).

Ahh thanks! I do that too, but I just go down once in the early fall

I agree with @pecmsg about the tankless coil bolts. They should be removed 1 at a time and coated with never seize. They should be checked for tightness yearly.

If you see and stains or dripping around the coil gasket in the future don't wait too long to get it fixed.

Other than that keep the boiler off if you don't need to run it.

Congrats on finding a good installer. Looks like you got a good job from what I can see.