No pump speed adjustment on Baxi boiler?

[durhamplumber]

The pump is dumb and runs at a set speed....the pump will always operate at a point somewhere along its "pump curve" ie. the line showing the relationship between flowrate and available pump head (pressure).
As you close down the radiator valves the operating point on the pump curve moves leftwards and upwards with a reduction in flowrate and an increase in pressure across the system.
For example if you were foolish to shut all the valves (ignoring the boiler internal bypass) the pump would be "deadheaded" and with zero flowrate the head pressure would top out at around 5 or 6m depending on the pump fitted.
Having a towel radiator open would drop the operating point back down the curve a little and likewise the excessive pressure could be relieved by the opening of an automatic spring loaded bypass valve (adjusted accordingly).

I am not being funny...He has a constantly open rad..I still do not see what he would gain faffing on fitting an extra bypass.

 

[Gasguru]

Not being funny either but can you read pump curves? Very few in this trade can.
The pump is applying excessive differential pressure across the remaining rad.

 

[durhamplumber]

Not being funny either but can you read pump curves? Very few in this trade can.
The pump is applying excessive differential pressure across the remaining rad.

I am sure I could if i tried!..how much pressure would be exerted on the rad? Never seen 1 have its tits blown off by constant speed pump

 

[jacoscar]

I am sure I could if i tried!..how much pressure would be exerted on the rad? Never seen 1 have its tits blown off by constant speed pump

I guess he means there would be a pressure high enough to make the water flow too fast

 

[durhamplumber]

I guess he means there would be a pressure high enough to make the water flow too fast

With what detremental effect? And what flow if there is no flow????

 

[ericmark]

Not being funny either but can you read pump curves? Very few in this trade can.
The pump is applying excessive differential pressure across the remaining rad.

I don't think the flow curve matters, what does matter is your idea will reduce noise and cure the guys problem. I do wonder about electronic TRV heads and will the thermostat controlling the boiler turn off the boiler at the same time as telling the heads to close?

I do wonder if on my system the TRV heads could cause cavitation? Pump on the return. When zone valve closes it auto turns off pump and boiler, but the TRV heads will only turn off boiler because linked to wall thermostat, and a few times noted on turning up wall thermostat the TRV heads have failed to follow.

 

[Gasguru]

I don't think the flow curve matters...

We've had 40 odd years of variable head pumps in domestic boilers...so I think you'll find it does.

At the moment we have a total horlicks in the domestic heating market....boiler manufacturers doing their thing (forced by the EU regulations), pump manufacturers doing their thing (again forced by the EU regs) and a bunch of " "disrupters" bringing out allsorts of weird and wonderful TRVS/apps to tempt the unwary who have little concept of heating theory. Much of this technology doesn't sit together, the net result being heating systems that often don't work particularly well, are noisy, cause damage to the boiler and in some cases use more energy.

 

[ericmark]

We've had 40 odd years of variable head pumps in domestic boilers...so I think you'll find it does.

At the moment we have a total horlicks in the domestic heating market....boiler manufacturers doing their thing (forced by the EU regulations), pump manufacturers doing their thing (again forced by the EU regs) and a bunch of " "disrupters" bringing out allsorts of weird and wonderful TRVS/apps to tempt the unwary who have little concept of heating theory. Much of this technology doesn't sit together, the net result being heating systems that often don't work particularly well, are noisy, cause damage to the boiler and in some cases use more energy.

Sorry I was being funny in my own little way, clearly it does matter, but what I was saying the reason was less important, it is the fact that adding a by-pass would cure the problem that is important.

And yes it seems I have one of those weird and wonderful TRV heads apps that don't work. Theory may be sound, but practice it does not work, theory when I move the wall thermostat dial or set a seclude then the TRV head should follow the Nest wall thermostat, but half the time is doesn't, so heating switches on but the TRV does not open.

As to if Tado has same problem as Nest/Energenie I don't know, but radiators should not switch off/on but gradually open/close so you should never really have a situation where all but one radiator is turned off, they should be gradually opening and closing so the temperature of radiators vary. But if the wall thermostat does not match the TRV's then there may be a problem.

But this has been a problem for years, my father-in-law had two zone valves one for CH the other for DHW in an S plan, and in theory the pump should not run unless at least one valve is open, however the micro switch stuck in so boiler running and valve closed so the pump was wrecked. Even back then a by-pass valve was needed in case a micro switch got stuck.

 

[Gasguru]

Nah...the bypass was needed due to the introduction of boilers requiring a pump overrun after burner shut down (when the 2 ports might be shut) and/or a low water content copper fabricated heat exhanger requiring a minimum flowrate to avoid kettling (very low thermal mass heat exchangers).