Horstmann 425 replace with Horstmann H37XL

[andrewthecoder]

Hey guys, it seems like you are all very helpful, and as I know very little about central heating/boiler systems (I still can't figure out whether I have a "Fully Pumped" or "Gravity Fed" system), I thought I would ask for help.

Recently, the hot water and central heating in my home stopped functioning. Luckily for me the problem was relatively minor - simply put, the motor which made the ancient Horstmann 425 Diadem tick stopped ticking

I did a search on eBay and bought a Horstmann ChannelPlus H27XL.
This was supposed to be a direct replacement, simply clipping onto the identical backplate and giving me new functionality, with the ability to set different times for different days.

Unfortunately the seller made a cock up, and sent me a Horstmann ChannelPlus H37XL. One number makes a huge difference, as my system only has two "channels" - hot water and central heating.
The seller has refused a refund/replacement and PayPal has refused to refund my money as it is too small an amount (£30).
Anyway, I've been looking at the wiring diagram for the H27XL and comparing with the H37XL, and I'm trying to work out if I can use this 3-channel unit with my 2-channel system.

Having a look at those, does anyone think I should be able to use the thing I've got with my system? If so, what wires should I have to change?

My backplate/wiring looks very much like this:

If this isn't sensible for somebody with little experience like me, what should I do - cut my losses and buy a real H27XL? Or is there a cheaper alternative?

Thanks very much, Andrew

P.S - Almost forgot. Any hints as to how to find out whether I have a Gravity fed or Fully Pumped system? My boiler is a "Baxi Solo 3 PFL 50", there are two large rectangular tanks in the loft, plus one smaller one (maybe 1/4 the size), and there is a cylindrical (usually hot) tank in a cupboard next to my bedroom. (the house is a bungalow)[/b]

 

[simond]

Your current backplate appears to have wiring to terminals 1, 3 and 5.

This would not allow your system to work properly on the CH, so I have to assume you have already 'had a go'.

In principle the 3 channel will work if you alter the pin layout but since the original wiring is suspect one would need to be on site to make any sense of it.

You wouldn't believe the number of issues we see on here from people buying heating controls off Ebay. Can't you buy them from a reputable source?

 

[andrewthecoder]

The photo I showed was taken straight from google images, it has nothing to do with me. Now I look back on it, that seems like a stupid thing to do - but as I don't have my camera for a few days, I figured I would show you *pretty much* what mine looks like (hence the caption - "pretty similar")

I haven't touched the wiring at all - in fact, while waiting for a reply I wanted to switch the water on and figured I could work out for myself how to turn it on using the controls on the H37XL unit in place - by switching "Zone 1" Heating on the unit to "ON", it switched the water on as I had hoped - you can see this quite clearly if you compare the wiring diagrams, pin 1.
Obviously this isn't ideal, you get a real mess if you try and use the timers, as each pin does something it isn't supposed to.

So, do I need to take a photo of my current wiring before doing anything else? Can't do so right now, my sister has my camera and she comes back from her holiday on wednesday.

Well, to be honest I don't trust eBay very much, so I do try quite hard to find things elsewhere first. But sometimes, price comes first, and the cheapest place I could find it from a "reputable dealer" was almost £60 from RS-www.
I figured half the cost was worth it for a small chance something could go wrong. Just a bit frustrating that technically nothing went wrong, the guy just made a cock up and picked up the wrong one from his stock.

Thanks for your response anyway, much appreciated.

 

[D_Hailsham]

Any hints as to how to find out whether I have a Gravity fed or Fully Pumped system? My boiler is a "Baxi Solo 3 PFL 50", there are two large rectangular tanks in the loft, plus one smaller one (maybe 1/4 the size), and there is a cylindrical (usually hot) tank in a cupboard next to my bedroom. (the house is a bungalow)[/b]

The Solo 3 PFL50 is intended for use with fully pumped systems only.

The large tank in the loft is the cold water feed to toilets, wash basins etc, and to the hot water cylinder, which is thing in the cupboard.

The small tank in the loft is the Feed and Expansion (F/E) tank for the central heating. The purpose of this tank is to supply water to the CH system when it is first filled or if any gets lost. It also provides somewhere for the CH water to expand into when heated.

Some people will, incorrectly, refer to your type of system is a "gravity" one. The term should really be used only for systems where the circulation through the HW coil is due to the change in density of the water when heated; i.e it is not pumped through the HW coil.

You should have a pump (Grundfos, Wilo) somewhere (in the boiler, if a system boiler) and either one 3-port motorized valve or two 2-port motorized valves.

 

[D_Hailsham]

Your HX37XL can be used, obviously with only one CH channel.

You need to make the following wiring changes:

1. Remove any links between terminals L, 2 and 5.
2. Disconnect the wire from terminal 4 and move to terminal 5.

 

[simond]

So you post a picture of a wired Horstmann backplate that isn't yours.

I know what a bl**dy Horstmann backplate looks like, for FFS.

I've seen some stupid posts on this site but this takes the biscuit.

 

[andrewthecoder]

Your HX37XL can be used, obviously with only one CH channel.

You need to make the following wiring changes:

1. Remove any links between terminals L, 2 and 5.
2. Disconnect the wire from terminal 4 and move to terminal 5.

Thank you very much.
That is exactly what I was looking for, and it seems to have worked perfectly.
There was no link between L, 2, 5.
I now have the three - channel unit working perfectly with only two channels.

As for your easy to understand explanation about my system, that was great, I'm a lot happier now I understand what is actually happening in my home.

Again, thankyou very much

~Andrew

P.S. @simond: I am sorry for making a small mistake and wasting, what, a minute of your time? Try not to be so harsh, yes looking back that was a stupid thing to post, but I've never been on these forums before so I didn't know what to expect, I was just trying to be helpful.
I'm sure there have been more pointless posts on these forums in the past.