Ancient sytem still working-change of timer/controller advice

16 Apr 2021
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United Kingdom
I have an ancient inefficient but very reliable system in my house and until I've saved up it will stay that way :)
It is pumped CH, gravity hot water, flow controlled with mid position valve.
So here is the specs if it helps (house was built in mid 70's and this is all original)
Boiler- Potterton Flamingo 50
Timer controller- Potterton Mini Minder (2ch mech)
Room thermostat- 3 wire
Hot water tank thermostat
Ma1 mid position valve MK1453 with Sunvic Dm5601 motor controller (earth,white,yellow,orange and blue wires)
wiring centre/relay box is Satchwell Sunvic RJ2802 in the airing cupboard with the hot water tank.

My MiniMinder (not an E but genuine Mini Minder) timer is not operating correctly as one of the ON timer 'tags' does not lock and just gets pushed until it butts against the OFF tag. I want to replace the timer but being obsolete they are going for asking price of £150 plus on the bay of evil.
I believe these were known as RWB2 type timers. Is there something modern that works with my system.
The MiniMinder has a six pin industry standard backplate and I did get a Siemens unit that was supposed to be plug and play but isn't, didn't even power up, and I think its the wiring.
I have N (black) L (red), i did say its old, Yellow in 3 and live (red) in 4. There is a blue wire not attached to any terminal and sealed within the single plate back box.
I understand (from reading so could be bollerx) that this was fairly standard for these old systems.
I don't expect to do anything more than it does now but need a new timer as its on 24hr at the moment.
Hope someone can help, and yes I know I need to modernise but I haven't got a spare £3k or whatever its going to cost to do that.

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Ok got it, Drayton. Thing is the Siemens was supposed to be compatible but the wiring I have in place doesn't match the unit diagram. Would a particular ACL unit be analogue enough to direct replace my Mini Minder?
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The Mini Minder is just a pair of switches, as are 99% of other 2 channel programmers.
Pretty much any 2 channel programmer will be suitable.
Whether it's analogue or digital makes no difference to anything.

Yellow in 3 and live (red) in 4. There is a blue wire not attached to any terminal and sealed within the single plate back box.
3 and 4 are HW on and CH on, and would need to be connected to those terminals in a new programmer.
L&N are the power supply to the programmer.

If there isn't a connection to HW off, it won't be possible to have CH only selected. HW will be on until the cylinder thermostat switches off - but that's evidently how it's been for years/ever so nothing will change there,
Thanks for the heads up folks.
Got the new timer/programmer up and running, there was a break just inside the insulation of one of the wires.luckily the drunk scousers/geordies who built the house in the 70's (this is based on facts but may include some dramatic addition) left plenty of wire to trim back and get a nice clean connection.
Thanks to all, will likely be back when I can afford to modernise with further questions demonstrating my ignorance in this field. I do know a lot about fixing cars and bikes in my defence.

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