Programmer / Timer replacement on an old boiler . Pump over run needed

[Mat29a]

I wonder if anyone is able to help. I have a ServoWarm Elite 50 Boiler . it is over 30 years old , and is extremely reliable and has never really broken down. This is a simple hot water boiler system . with a pump and thermostat all in the housing. there is no room thermostat. so all it does is, send hot water around in a single circuit serving the emersion tank and central heating. The boiler thermostat is controlled by the max//min settings in the honeywell modulec unit and when hot enough the boiler turns off, and on again etc until the timer goes off. then the pump overrun continues for a little while.
My problem is, the programmer , a Horstmann 424 Emerald ( discontinued ) clock is faulty due to a slipping/worn plastic gear wheel and required manual switching. I need a replacement programmer .. This clock was a bespoke unit for this boiler, with a built in pump over run switch . Horstmann UK recommended a modern version , a 425 Coronet, but it has no pump overrun ( so they cannot advise on it ) . In which case I could just get any single switch timer/programmer for hot water only.. and connect some delay relay unit as pump overrun. Does anyone know if there is such a thing as an external relay / pump overrun unit that can be connected from a new programmer ( any of the above) to the pump?

 

[heatservice]

Call it a day as your uncontrolled system is no better than a gravity one, you could reduce your running costs buy 30% + with a new boiler and controls.

 

[stem]

You could wire the switched output from the new timer that is live when the timer is 'on' to the coil of a suitably rated 'delay on de-energise' relay. Then wire the contact to a permanent live and the pump. That would keep the pump running for a preset time when the timer went off.



Or you could use a suitably rated timer designed for use with a fan. A quick internet search came up with the example here. It's designed to provide an adjustable 'run on time' and has a 5A rating.

This would allow you to keep the current system running until it was convenient to upgrade it.

 

[heatservice]

You could have the pump wired via a pipe thermostat attached to the flow so it would continue to run on until temperature dropped.

 

[Mat29a]

Thanks for all your input..
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Stem - is it a kind of time delay relay you might be referring to ? ie connect between the programmer and the pump.. I have difficulty finding one any idea?.

heatservice - with your pipe thermostat, presumably wiring would be from Programmer to the thermostat , then to the pump? - I am not familiar with a pipe thermostat , have you any in mind, or suggesting one ? could be interesting
----
i just seen one on eBay, is this probably one ? I am trying to figure out the wiring?
HONEYWELL L641B 1004 LOW LIMIT PIPE THERMOSTAT

 

[heatservice]

The pump need to switch ON with the timer but by also putting a permanent Live to terminal C on pipe stat and conect terminal 2 on pipe stat to pump Live and set the stat to 60C should do it.

 

[stem]

Stem - is it a kind of time delay relay you might be referring to ? ie connect between the programmer and the pump.. I have difficulty finding one any idea?.

There's an example here. but it would need to be mounted in an enclosure.

The fan timer link that I posted earlier, see here, does the same thing but comes with an enclosure.

The pump need to switch ON with the timer but by also putting a permanent Live to terminal C on pipe stat and conect terminal 2 on pipe stat to pump Live and set the stat to 60C should do it.

The timer is also controlling the boiler. So, if you were also connect a permanent live to 'C' it will also be connected to the boiler and keep it 'on' permanently. The thermostat could be wired to make use of its changeover contact to avoid this as below.



1. When the pipe is cool (the position shown in the diagram above) and the timer switches on the boiler, the pump will also start as the thermostat connects it to same switched live from the timer.

2. As the pipe heats up, the pipe thermostat contact will switch over, and the pump will now be connected to the permanent live.

3. The timer goes 'off' as does the boiler, but the pump will continue to run from the permanent live.

4. The pipe cools and the thermostat switches over back to the timeswitch live which is now 'off' and the pump stops.

 

[Mat29a]

thank you heatservice, & stem..

:heatservice is the pipe stat you are referring to the Honeywell L641B I mentioned? or pipe stats are pretty standard.

:stem - I am looking at your link to Schneider Electric OFF Delay Single Timer Relay, Screw, 0.1 s → 100 h, SPDT, 2 Contacts, SPDT
and also the fan timer.

Most probably get a horstmann 425 coronet, and then study the above 3 pump over run options and try draw up some draft for them .
Consider how the 2 existing wires fit in. ie one cable from the pump ( B/N/E)
and 1 cable from the boiler ( Brown, Neutral , RED, E)

 

[Mat29a]

I am looking at the red wire in the cable from the boiler. it is connected to the "solenoid" terminal of the timer, and leads to the timers pump overrun microswitch unit ( see 2 red circles ) and joined to the 2nd red circle is on a strange ( i think), semi conducting plate that heats up the adjacent stat plate causing it to bow, and release the microswitch, and switching on the pump.

Is it fair to presume that this red wire will be dormant in the new configuration we are discussing

 

[stem]

I agree with your reasoning, but without a wiring diagram I can't say for certain. These things were a bit before my time.

 

[Hot&Cold]

is it not possible to disconnect the mechanical timer wires only and adapt to a new external time clock ?

Mat29a do you have a pdf or link to the boilers installation & servicing instructions ?

Edit.does the boiler have an overheat device

Not seen one of them boilers for years,they always had the burn scorch mark on the timer fascia

 

[Mat29a]

thanks stem ..

I agree with your reasoning, but without a wiring diagram I can't say for certain. These things were a bit before my time.

I wonder if the following images can be of any help to establish whether or not the Red wire from the boiler can be discarded in the new config. If so. then there are only 2 cables to consider: to Pump ( L-N-E ) and to Boiler ( L-N-E with Red sealed off )

The timer 'Solenoid' terminal is where the RED wire connects - I try to illustrate it in the 2nd hand drawn image . Basically this is only live to heat up the microswitch stat to release the switch and supply power to the pump. once switch is released the red wire connection is off. Why this red wire needs to come from the boiler puzzles me. ( probably low voltage? at a guess. dont know)

 

[Mat29a]

Hi Old&Cold.. thank you for your help .. pls see my [] responses below

is it not possible to disconnect the mechanical timer wires only and adapt to a new external time clock ?
[ yes i am trying to replace this with an external or any timer that works, and we are discussing about how to get around the pump over run problem
by installing some kind of relay between the new timer and the pump.

Mat29a do you have a pdf or link to the boilers installation & servicing instructions ?
[ too old to find on google I think. but please see technical data in my post above ]

does the boiler have an overheat device
[ yes the boiler has overheat switch, you can see it in the overall image - a round black dome with a tiny red push switch that pops up if boiler overheats. Over heating would occur rarely when the pumper overrun cheap (£2) micro switch wears out once every 8 years or so. ]

Not seen one of them boilers for years,they always had the burn scorch mark on the timer fascia
[the Boiler is about 30yrs old. very simple and nothing to breakdown and never did. heats up water in one circuit to serve emersion tank & c/heating.
The timer plastic casing has scorch mark built up over the years due to heat from the built-in pump overrun stat plate. it is a small plate and gets very hot ... ]

 

[AlanE]

Is this the system where the boiler is hidden behind a radiator?

For programmer look here - https://www.ebay.co.uk/itm/HORSTMAN...I6Mywic28iOjE1MDAsImMiOjIwNzE1fQ==&rmvSB=true

 

[Mat29a]

Is this the system where the boiler is hidden behind a radiator?

No this is just like any normal mounted boiler. with timer and pump at the bottom.

Is this the system where the boiler is hidden behind a radiator?
For programmer look here - https://www.ebay.co.uk/itm/HORSTMANN-424-EMERALD-BRAND-NEW-OLD-STOCK-NOW-OBSOLETE-/132475198765?clk_rvr_id=1496459255124&utm_medium=cpc&utm_source=twenga&utm_campaign=twenga&utm_param=eyJlcyI6MCwicyI6OTcyMDIzNywiY2kiOiIwMzY2ZWRlOTMwNTJjNTI1ZDlhNjA1ODdmMmQ2MjVkMiIsImkiOiIxMzI0NzUxOTg3NjUiLCJ0cyI6MTUyMzQ2NjY5NCwidiI6Mywic28iOjE1MDAsImMiOjIwNzE1fQ==&rmvSB=true

This ebay unit is the same 424 Emerald model but it has no pump overrun. This boiler has a bespoke 424 emerald , same design but they added a clever pump over run with microswitch. So my replacement will need an external relay/overrun connection to the pump.