Please explain my CH system! (Lots of questions)

[asktoby]

I don't know the first thing about plumbing!
I've taken a photo of the system in my house and labeled it up:
http://www.asktoby.com/miscimages/plumbing.jpg

• 
  1: Honeywell thermostat, adjustable.
  2: Heatrae Sadia Megaflo Thermostat
  3: Thermal cutout
  4: Honeywell motorised valve
  5: Honeywell motorised valve
  6: Grundfos Selectric pump
  7: Tap
  8: Temp/Pressure relief valve
  9: Knob
  10: on/off

What do all the above things do?
Which device heats my radiators: The megaflow or the boiler?
Which device provides hot tap water: The megaflow or the boiler?
Why do I need two water heating devices?
What does the knob on the downstairs boiler do?
Following a recent new shower install by a local builder, I've noticed that the tap water is permanently very hot. I've tried turning the Honeywell thermostat (1 on photo) to minimum but the tap water is still scalding hot. Is the thermostat (1) broken, or has the builder left something wrongly adjusted?

 

[Boilerman2]

1) Hot water thermostat (when using gas boiler to heat Hot water)
2) Immersion heater (when NOT using gas boiler to heat Hot water)
3) Overheat device, shuts off Motorised valve to hot water if excess temperature is detected
4&5) Motorised valves 1 each for Heating & Hot water
6) Circulation pump (moves water around the system from the boiler to heat radiators & Hot water


What you haven't found is the Programmer (either in airing cupboard or Kitchen?
This is what actually controls the Heating & Hotwater
by entering what times of day you want the hot water and or heating to be operational

 

[Agile]

I think all those questions are answered in the FAQ on this site!

 

[seniorservice]

Sorry to hijack. Can someone explain what the can shaped thing is in the left hand photo? What does it do?

Am I right in thinking it's plumbed into the flow from boiler, but what are the other pipes into it?

I've got one, but always wondered what it did?

 

[Armo74]

The can shaped thing i think your talking about looks like a air seperator. There is the flow from the boiler, the vent pipe and the cold feed from the f/e tank, and it does exactly what is says on the can

 

[seniorservice]

The can shaped thing i think your talking about looks like a air seperator. There is the flow from the boiler, the vent pipe and the cold feed from the f/e tank, and it does exactly what is says on the can

Thanks for your reply.

What air is it seperating? Where would the air be coming from?

My brother has a similar system, but no seperarator. What is different about my system to need a seperator fitted? How does it work?

Apologies for all the questions and more hijackings than a 1970s Israeli Jumbo Jet.

 

[asktoby]

OK, I've done some more reading now. Are the below statements correct?

a) Electrical immersion heater in Megaflo should be turned off. It's just for high-hot-water-demand emergencies, e.g. showers when guests visiting. Gas boiler is cheaper for heating water so should be used day-to-day.

b) Knob (9) on kitchen boiler adjusts the temperature of both the radiators and the hot tap water? What if I want hot radiators and cooler tap water?

 

[Boilerman2]

Leave the knob on the boiler turned up about 3/4's , thyis controls the temperature of the Rads and primary circuit, generally the higher this is set the more efficient the system will be,

To control the temperature of the Hot water at the taps adjust the honeywell thermostat (ITEM 1) in your picckies

 

[asktoby]

Thanks for the info.

"generally the higher this is set the more efficient the system will be"

Should I not just set it to 100%, to get the best efficiency?

Also: Do you think it's worth me lagging the hot exposed pipes in the picture?

 

[r896neo]

you can but will potentially burn yourself on the rads

 

[asktoby]

Just for completeness I've compiled all the info in this thread into a single image here:
https://kuula.co/post/7P9V6

 

[mogget]

#1 is the expansion relief valve for the hot water,
#2 is the pressure reducing valve for the cylinder, this keeps pressure within the hot water system within design limits.

What you have labelled as "pressure release valve" is actually known as a Temperature and Pressure Relief Valve (TPRV)

 

[asktoby]

Thanks! I've added that detail.