No DHW unless CH is on

[ExBandit]

Hi Folks,

My parents have a heating system as follows: (Fitted by British Gas).

Ideal Mexico Super 2 RS50
Horstmann Tiara H425 controller
Room stat
Fully pumped system
3 way mid position valve

Their issues appear to be 2 fold.

1. Ever since this system was fitted the DHW was only available when the CH was on or in other words the CH & DHW are NOT independant.
I understand there are 2 ways of wiring the Tiara H425 controller i.e. For a pumped system or a gravity system - would i be right in thinking that this may have been wired for a gravity system which i understand would result in the 'non independant' operation of the controller?
If the DHW is seleted on 'constant' nothing happens - only when the CH is activated does the DHW appear to kick in. They normally set the room stat to zero so that the radiators don't actually heat up.

In addition... they haven't used the heating all summer (we had a summer?) and the first time they used it (recently) they turned the room stat up quite high - now when they put the CH on to activate the DHW they can't stop the rads heating up - even by setting the room stat to Zero.

I'm only an IT dude with limited plumbing/heating experience and can see that there are many 'possible' areas of failure e.g. the controller/room stat/cylinder stat/mid position valve. I was wondering if anyone may be so bold as to suggest a 'Probable' point of failure ??

After confirming that the controller is wired up correctly (i now have the diagram) i think i may try (in the following order)

1. bypassing the controller to see if the DHW fires up the boiler - if yes the controller is faulty?
2. If the DHW still doesn't fire up - bypass the cylinder stat?

3. unsure about the Mid position valve as i've already been manually adjusting with no effect.



Any pointers gratefully accepted !

Ian

 

[gas4you]

Sounds as though it is not wired up correctly to me, even though you say you have checked it.

My first thought is that it is wired for gravity but wired back to front ie the ch is on the hw terminals and vice versa.

IF it is wired up correctly check that there are no dip switches that need setting for fully pumped.

I do not know this timer so just generalising on what may be the problem.

 

[ExBandit]

Sounds as though it is not wired up correctly to me, even though you say you have checked it.

Sorry, i may have mislead you when i stated "After confirming that the controller is wired up correctly" .. i meant that i WAS going to check it and then carry out the other steps...(haven't done so yet)

Have just checked the installation manual of the controller and there's no mention of any dip switches....

Good point about the reversed wiring !

I think the 1st step is to establish that it's wired correctly....

Thanks for your response.

Ian

 

[D_Hailsham]

Have just checked the installation manual of the controller and there's no mention of any dip switches....

It does mention an interlock for gravity systems - see page 2. 425 Installation Guide

 

[ExBandit]

Have just checked the installation manual of the controller and there's no mention of any dip switches....

It does mention an interlock for gravity systems - see page 2. 425 Installation Guide

Unsure of what you're pointing out re: Interlock... ? Isn't this purely for the benefit of gravity systems?

The switches aren't interlocked but yes i did interlock them just to see if it made a difference - unfortunately not..

Apologies if a dip switch = interlock...in IT it's something different...

Thanks for your post

Folks, I'm off to Devon until Tuesday (bike trip) so won't be able to respond to any posts after tonight. Please don't think i'm being ignorant when i don't respond until Tuesday

 

[D_Hailsham]

Unsure of what you're pointing out re: Interlock... ? Isn't this purely for the benefit of gravity systems?

The switches aren't interlocked but yes i did interlock them just to see if it made a difference - unfortunately not..

Apologies if a dip switch = interlock...in IT it's something different...

Some heating programmers use dipswitches for the gravity interlock. Your one uses a mechanical interlock. Gas4You suggested that it might have been accidentally set for gravity HW. But you have checked and it isn't. So that eliminates one possibility.

Hope you had a good trip!

 

[ExBandit]

Thanks for the responses...

OK... i've checked out the wiring for the controller and it's definitely NOT wired as per the instructions for a fully pumped system and can see that by selecting DHW 'only' wouldn't actually do anything as there's no wiring to the controller to call for HW! (Terminal 1 in controller).

If my parents will agree to it i'm going to try and identify the wires coming up into the controller and re-wire it so that the DHW can be called independently of the CH.

If anyone just happens to be bored and is feeling helpful then this is what the current wiring set up is at the controller.

Cable 1 (Grey)

Red - to L (on controller)
Black - to N (on controller)
Earth - to Earth (on Controller)

Cable 2 (Grey)

Red to Connection 4 (controller - CH call)
Blue to N (on controller)
Earth to Earth (On controller)
Yellow to Brown on Cable 3 ??? (by way of block connector)

Cable 3 (White flexible cable)
Blue - to N (on controller)
Earth - to Earth (on controller)
Brown - to Yellow on Cable 2

Looks daunting in writing but with a pencil 'n' paper maybe someone could help identify them? Don't want much do i?




I think the other issue of not being able to control the room thermostat is simply a faulty room stat - and at under £10 has to be the 1st thing to swap out.

Thanks again folks...

 

[D_Hailsham]

Cable 1 (Grey)

Red - to L (on controller)
Black - to N (on controller)
Earth - to Earth (on Controller)

This is the power in to the controller.

Cable 2 (Grey)

Red to Connection 4 (controller - CH call)
Blue to N (on controller)
Earth to Earth (On controller)
Yellow to Brown on Cable 3 ??? (by way of block connector)

What does the other end of the red connect to?

Cable 3 (White flexible cable)
Blue - to N (on controller)
Earth - to Earth (on controller)
Brown - to Yellow on Cable 2

So the yellow of cable 2 links to the brown of cable 3. Is that all that happens? Can't see the point of that unless they are connected to something else!

You mention a cable connector. Is this just an isolated connector or do you have a wiring centre (junction box) into which everything is connected?

Here is a wiring diagram showing how a mid-position valve system should be wired up:

Compare this with your current wiring and you should be able to find out what's wrong.

PS If you need to post more info about your current wiring, pleas say what each end of every wire connects to. Also, colours are not standardised so don't assume anything.

 

[ExBandit]

Thanks very much for taking the time to post that information - very much appreciated!

(Been looking all over t'internet for a pic like that - thank you!).

The problem i have is actually trying to determine where the other ends of the wires are! No doubt the right person with the right tools could do that in a flash...

So is the theory such that ...

1. Power directly into the controller - From fuse spur?

2. Does the controller then feed back to the boiler directly - to complete the circuit when calling CH or HW?

3. Boiler connects to the connection block up in the airing cupboard (which connects the pump/room stat/cylinder stat/mid position valve?

So many questions..... so little time

 

[ExBandit]

Just for clarification -

You mention a cable connector. Is this just an isolated connector or do you have a wiring centre (junction box) into which everything is connected?

This is a single terminal block connector inside the controller.

There is a wiring centre up in the airing cupboard as per previous post..

 

[ExBandit]

...and just like elderly parents do.... they produce the boiler's installation manual which has been gathering dust and forgotten about

I'm hoping that with the boiler wiring diagram & controller wiring diagram i can suss it out....

Many thanks for the input chaps!

 

[D_Hailsham]

I'm hoping that with the boiler wiring diagram & controller wiring diagram i can suss it out....

Post back to this topic if you need any more help.

 

[ExBandit]

I mentioned that the issue was 2 fold.....

1. Dodgy controller wiring.
2. Heating not being controlled by thermostat.

Issue 2 has now been resolved !! It turned out that the mid position valve wasn't performing correctly i.e. it was opening/closing the valve as per thermostat call/satisfied but wasn't FULLY closing off the hot water call.

Remedied by removing the top off the MPV and applying a bit of additional pressure to the mechanism to ensure that the valve was being fully opened and closed when required.

Will no doubt need a repacement valve soon but nice to know what that particular issue was...

As for the wiring..... parents are happy enough to have the system 'as it's always been' (wired incorrectly) as they've gotten used to it... oh well..

Sincere thanks for the responses...
Ian

 

[ExBandit]

Just for info:

Having traced all the wiring it's plain to see that the controller wasn't originally wired to enable the HW & CH to work independantly.

Just thought i'd post this in case it helps anyone else with similar issues...

many thanks to peeps that assisted in suggestions....

Ian