Baxi Megaflo 28 System ErP General Query/Help

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dark_knightuk

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Hi!

So I have just moved into a new house and it has the above boiler fitted and I am trying to understand it as best as possible.

The control is set to water and central heating, Normally there is a temperature control for the central heating and then one for the water, but this is combined.

The issue I am finding is that if we want the central heating to be warmer, the water out of the tap becomes boiling as well?

We have Siemens controls (1 on the basement floor and 1 covering the upper floors I think) but they don't control the temperature, we also have Honeywell thermostat controls but they just don't seem to do anything (1 on the basement and 1 on the first floor) controlling the temperature from the boiler itself raises the temperature correctly?

1st-floor siemens control:

KEtmuFJ.jpg


So this has hot water and central heating control. If I want the radiators to be hot, I just run the central heating side of things on the right, if I want to heat the water I run the one on the left? My wife seems to think the central heating only pumps out hot when both the HW andCH are running at the same time?

1st-floor Honeywell thermo control:
lVBgrDy.jpg

Doesn't seem to do anything?

Basement siemens and themo control
QkkolfT.jpg

This is near the boiler but has no hot water control and I assume this controls the central heating in the basement area as it's on that floor?

Boiler control:
0xZNPxW.jpg

When the siemens triggers on its set times, the boiler comes on and the LED shows the temperature, I just don't understand how to control the water temp separately?

Water Tank:
GZjgHyQ.jpg

We have had it a few times where while the shower has been running the water temp has dropped off a lot. I assume its because the water tank has run out of water? In this case does the boiler have to be running from them on to provide direct hot water and does the tank fill up on its own and get heated after a period of time.

Apologies for the barrage of newbie questions, first time I have lived in a house of this size, with this kind of system and I just want to get my head around it all!
 
Check for the immersion heater being left on for the really hot water. The basement programmer appears to be for heating only, so could be underfloor heating or indeed a separate zone. It could be that when you have the heating on that it’s being distributed to the cylinder as well.
 
The Novice said:
Check for the immersion heater being left on for the really hot water. The basement programmer appears to be for heating only, so could be underfloor heating or indeed a separate zone. It could be that when you have the heating on that it’s being distributed to the cylinder as well.
Click to expand...
Right I will have a nosy at this, there is defo no underfloor heating. I have set the hw function to only run in the morning as the tank should keep the water warm for a couple of days I would guess.
 
dark_knightuk said:
the tank should keep the water warm for a couple of days I would guess.
Click to expand...

Guess again. Once heated, it will deplete from usage, or if it was just sat there it would probably last until the evening or the next morning at best, depending on the insulation thickness.
 
The Novice said:
Guess again. Once heated, it will deplete from usage, or if it was just sat there it would probably last until the evening or the next morning at best, depending on the insulation thickness.
Click to expand...
ah that's fair enough, IT runs in the morning for a few hours. I just don't need the water to be that boiling hot its crazy
 
If it runs in the morning for a few hours, then I’d be looking at the immersion being on as well, and the cylinder thermostat is set correctly.

To give you an idication, I have mine set for approx 45 mins in the morning and that’ll generally last until it comes on again in the afternoon when all the showers and baths are taking place. The morning period will keep for hand washing and dishes. Check what I’ve said and report back.
 
If that’s the case, then the cylinder may have been an upgrade and could be a direct cylinder, which doesn’t run from the boiler, only immersion’s - so check these are set to correct temperature - 60-65 degrees is best to kill any form of leginonella bacteria. If what is coming out of your taps is in this region then the temp is fine and you need a thermostatic mixing valve or tap to blend the water to prevent scalding.
 
The Novice said:
If that’s the case, then the cylinder may have been an upgrade and could be a direct cylinder, which doesn’t run from the boiler, only immersion’s - so check these are set to correct temperature - 60-65 degrees is best to kill any form of leginonella bacteria. If what is coming out of your taps is in this region then the temp is fine and you need a thermostatic mixing valve or tap to blend the water to prevent scalding.
Click to expand...
Ah sorry I am a bit confused, if there is no thermostat on the cylinder, it would be using the temperature set by the actual Baxi boiler to heat the water? So if that is set to 70 that means the radiators are pumping out heat and the water in the tank is being heated to 70c as well?
 
If it’s separate heating from the hot water, then 70 will be fine for radiators. The immersion heater if it’s a direct system will heat the water up and a thermostat will be under the cover cap of immersion, and this is what it will heat to.
 
This is the thermostat that controls the temp of the water in the cylinder.
Annotation 2020-03-18 122212.png


Check that the two port valve isin't stuck open, very common fault on unvented cylinders.
 
picasso said:
This is the thermostat that controls the temp of the water in the cylinder.View attachment 186235

Check that the two port valve isin't stuck open, very common fault on unvented cylinders.
Click to expand...

Ok so I just went down and had a look:
SJSIBfs.jpg


SO that is indeed the thermostat, so I can adjust that to adjust the temp in the water tank. It looks like I will be guessing the actual temperature heh. The thermostat wires into the Honeywell box just behind it on the wall (picture below)
Also, the black circle thing under it has a wire going from it that terminates in a 3 pin plug....that isn't plugged into any socket?

tJyk52T.jpg


So, in that case, the Baxi boiler is actually only doing the central heating, it has nothing to do with the hot water coming from the taps in the house?

So I have just set the Siemens control on the first floor to come on with CH only and I barely get any heat out of the radiators and the boiler doesn't even turn on, but when I set that siemens control to turn on HW and CH the boiler fires up and I get solid heat out of the radiators?
 
The black circle thing is an immersion heater, it’s only used when your boiler breaks down, try turning the cylinder stat up and the central heating off and see what happens, the boiler should be set at 75c as the cylinder stat should control how hot the hot water gets.
 
picasso said:
The black circle thing is an immersion heater, it’s only used when your boiler breaks down, try turning the cylinder stat up and the central heating off and see what happens, the boiler should be set at 75c as the cylinder stat should control how hot the hot water gets.
Click to expand...

Will try and report back

So that leads onto the question of why on the siemens control do I need to turn on CH and HW to get the boiler going for the radiators? APologies you can tell I am clearly confused lol
 
Because you probably have a faulty 2 port valve (that's the silver boxes on the pipes) they can give strange symptoms when the stick open/shut or the microswitches stick or don't contact.
 
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