Help me decipher my boiler/heating system?

HungryHippos

HungryHippos

HungryHippos

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Just got a new house, and unlike my old one, this has a more complex system.

My previous one was a simple combi-boiler, with dual zone thermostats. Need hot water it just fires up. Need heating, it fires up for that automatically as well.

Here are some images from my new one:

http://imgur.com/a/7z9Nm

It seems to have a Potterton condensing boiler, in pics #1 and #2.

Pic #3 is a Honeywell control unit with model ST9100C.

Pic #4 is one of the two Honeywell CM907 thermostats (one upstairs one downstairs). This looks reasonably similar to my old zone thermostats.

Pic #5 and #6 are of the bit water tank in the cupboard upstairs.

Could really use some help understanding how this all interacts!

I'd guess for hot water, the big tank is used upstairs. I think there is a smaller tank above it that may be for a smaller heating load. Does the hot water tank need the boiler as well, or does it just use electric to heat it?

I'd assume the condensing boiler is crucial to heating, but the water being used by the heating would not be drawn from the big water tank?
 
The boiler doesn't heat the water in the tank...Per se

It heats water that is in a coil in the tank. Those pipes then heat the surrounding water in the tank

There will/is/should also be an immersion backup on the tank to heat the water should your boiler breakdown.

Somewhere, Generally near the boiler you' have 3 valves. 1 for each zone (thermostat) and 1 for hot water.
 
Its an unvented system by the look of it.

The potterton boiler will do your central heating and hot water - but the hot water isnt instant like with a combi boiler.

The heatrae sadia cylinder is for hot water only. Its indirectly heated by the primary (boiler) coil (those are the pipes you can see on the bottom left of the photo). The pipe with a blue collar is the mains cold supply to the cylinder and will top it up as hot water is drawn off. The pipe out the top is the hot water out to your taps etc. The grey panel thing is usually where they hide the immersion heater for backup / ad-hoc hot water should the boiler be offline / broken.

The hot water cylinder is mains fed (usually) but can be fed from boosted tanked water but that is unusual in a domestic house.

Also what is the tank above the cylinder? Are you sure its a tank and not an expansion vessel? (Photo would help). Generally heatrae sadia units use internal expansion but I have seen them fitted with external vessels. It could be an expansion vessel for the boiler too. Generally blue and white are potable water expansion vessels. Orange and red are for the heating system.
 
HungryHippos said:
Thanks guys, I took some pics of the tank above the cylinder.

http://imgur.com/a/wsc1X

Sorry for the first pic, my camera sees the light above as the same lumens as a thousand suns, but you should get an idea where the tank sits in relation to the cylinder.
Click to expand...

As suspected - its an expansion vessel and fitted the right way around too!

That vessel has either a rubber bladder or diaphragm inside that expands when pressure builds. Its basically part of the safety mechanisms of the hot water cylinder. The other one is the pressure release valve on the side of the hot water cylinder which will vent to drain via a tun dish.
 
Thanks guys for all the help, so if my understanding is right from all that has been said here:

1. The boiler has it's own control unit, that controls when it comes on for hot water. It will then heat the water that gets stored in the cylinder and is drawn from the cylinder when you use hot taps/showers/central heating etc.

2. The cylinder has it's own immersion heater in case the boiler is busted, but one assumes it's not used generally. Is there a way to confirm that if the immersion heater is in use or not? I assume it's reasonably expensive to run compared to the condensing boiler. Maybe even a way to disable the immersion heater so I know it can't use it without my implicitly turning it on?

3. The thermostats will use hot water from the cylinder, but wont directly "ask the boiler" to heat water like my old combi did? In that case I'd assume it would be best to program the hot water to come on an hour or so before you intend to put heating on?

Probably missed some understanding on the above.
 
1=yes
2= follow those wires that are coming out of the grey thingy.. They should lead to a switch/Isolator.
3= Not sure what you mean But. The Thermostats tell the boiler what to do. The thermostats wont have anything to do with hot water apart from tell the boilers when to heat the water.

Our boilers heat the water at 7am but its still red hot at midnight. I think at about 55Deg if you turn your boilers off then 24hrs later the water will still be above 50Deg. They are very efficient nowadays. There will also be a Stat on the cylinder somewhere (poss under the grey cover) This will tell the boiler if the water temp goes below a certain point. Ie When you draw off hot and it fills with cold

Is they system working as you want it too.

I wouldn't really be fiddling with anything unless its NOT doing what you want.
 
Not moved in officially yet, main furniture is moving across this weds, just wanted to get a handle on how it was working before I needed to use it. Won't really be using the heating for a while as well as it's still pretty warm out there.
 
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