System boiler - should HW automatically come on when CH is turned on?

[mjgreen81]

Hi all,

I moved in to a new house earlier this summer which I believe has a system boiler (I'm used to a regular boiler in my old house).

The HW is programmed to come on twice a day.

This week (as I am sure a lot of people have ) , the CH went on for the first time. I noticed that when the CH is turned on, the HW also comes on automatically (even if it is not programmed to come on at this time).

I did a bit of reading around how a system boiler works, and from my minimal understanding I *think* that this is expected behaviour.

Would someone be able to confirm if this is expected and if they wouldn't mind giving a brief dummies explanation as to why, it would be appreciated (I like to learn!).

Many thanks

 

[fixitflav]

Hi all,

I moved in to a new house earlier this summer which I believe has a system boiler (I'm used to a regular boiler in my old house).

The HW is programmed to come on twice a day.

This week (as I am sure a lot of people have ) , the CH went on for the first time. I noticed that when the CH is turned on, the HW also comes on automatically (even if it is not programmed to come on at this time).

I did a bit of reading around how a system boiler works, and from my minimal understanding I *think* that this is expected behaviour.

Would someone be able to confirm if this is expected and if they wouldn't mind giving a brief dummies explanation as to why, it would be appreciated (I like to learn!).

Many thanks

It shouldn't happen in a new house (assuming it is new, not new to you). I'd expect there to be a 3-port valve (W or Y-plan) or two 2-port valves (S-plan) to give CH or HW or maybe both. If you have that, you might still get your symptoms, if a valve has failed. Or possibly wired wrong.

 

[CBW]

If you’re unsure if the setup as described by @fixitflav then post some photos of what you have: cylinder cupboard, programmer etc.

 

[ianmcd]

Sounds like you have a gravity HW system

 

[fixitflav]

Sounds like you have a gravity HW system

Correct me if I'm wrong, but I don't see how that's possible with a system boiler

 

[ianmcd]

Correct me if I'm wrong, but I don't see how that's possible with a system boiler

My apologies , meant to say sounds like the programmer is set to Gravity HW

 

[fixitflav]

My apologies , meant to say sounds like the programmer is set to Gravity HW

No problem, be good to hear from the OP what kit he has.

 

[mjgreen81]

Sorry for the delay guys, got a sick toddler which is taking up all my time.

Below are the images of my system. I believe it is the original system installed with the house (about 20 years old). It has been serviced each year.

Please let me know if you require any further information.

 

[CBW]

Is it coming on at the programmer or just by itself?

 

[mjgreen81]

Is it coming on at the programmer or just by itself?

At the programmer. The HW LED on the programmer lights up when the CH automatically comes on via the set time or if I manually press the HEATING ADVANCE button.

 

[CBW]

Check the programmer isn’t set to Gravity as mentioned, failing that might be new programmer time.

 

[Johnmdc]

You have a thermal store.
It has to be heated up for the heating to work.
So your system is operating as it should.
You cannot have the heating on on it's own with that type of system.
The programmer has been set to gravity correctly.

 

[DP]

Might be a good idea and prudent to fit a double check valve on the flexi pipe to top section of the cylinder

 

[mjgreen81]

You have a thermal store.
It has to be heated up for the heating to work.
So your system is operating as it should.
You cannot have the heating on on it's own with that type of system.
The programmer has been set to gravity correctly.

Thank you, this is what I suspected

 

[ericmark]

I seem to remember there were both dip switches and physical stops which needed to be set so you could not select central heating only. Looking at the installation instructions. It seems there is a link marked G for gravity and P for fully pumped, @Johnmdc says it is a thermal store, and he likely knows more than me, I have only seen thermal stores with multi-fuel or electric central heating, the idea is many ways to heat but all use same distribution system so solid fuel, solar, gas/oil, and electric all can heat the same heat store which then sends the heat to same radiators, brother-in-law had it with last house, but when he looking at fitting it in his new house the installation price was silly.

It is also used with solid fuel as most solid fuel fires/boiler need to run at a set rate, in order not to have particular emissions, so often run once a day, until heat store hot, then let go out, but in brother-in-laws house the heat store was twice the size to what you show, which was why so expensive, as the floor needed reinforcing to take the wait, and the tanks always upstairs so if there is a power cut the heat is still transferred from the fire, one does not want to rake out a solid fuel fire if there is a power cut.

So it seems some thing missing in your tale? Or it's not a heat store, simply can't see why one would fit a heat store with a single gas boiler?