Y Plan Pump Overun

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maselec

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Hello everyone,

I've got a job to do for a gas fitter I know, received the info last week and was told it was to swap the programmer for another and wire in a new pump on a y plan system.

The gas fitter has since mentioned that the pump needs to overrun after the stat has stopped calling for heat. I've worked on a few heatings before but not for a long while and this is new to me. My understanding of it, is that the permanent live for this overrun should come from the boiler and that the boiler should have a terminal for this. However, according to the gas fitter, this is isn't the case. He says the boiler he has fitted (I won't know which until tomorrow morning) doesn't have this and that previous electricians he has used have just taken a permanent live from the wiring centre. I don't see how this could possibly work but he is adamant.

Am I missing something obvious? I've even Googled and downloaded a few wiring diagrams but they all confirm that the overrun feed comes from the boiler. I've to meet the guy tomorrow and don't want to look stupid (why change the habits of a lifetime?!) so any pointers and advice is greatly received.

Thanks.

 
Agreed.

A live feed from anywhere isn`t the answer. The only "variant" on this, is for the pump to come on with the zone valve switches - so the pump will run if the valve is open - the boiler should regulate its own temperature, based on the return temp in the pipework - but for that to work efficiently, the pump must be running.

However - when demand from a timeclock, t`stat or other control in the primary wiring closes the zone valves the pump will stop. Which is just as well, otherwise the pump is pressurising a closed pipe - which, over time, will damage the pump.

 
What's the purpose of the overrun?

As already mentioned, if the valve has shut the flow won't go anywhere useful. Though a 3 port valve can never "shut" it goes either to the heating or HW or both.

Talk to the plumber and consider putting an automatic bypass valve to allow flow to go somewhere during overrun if all valves are shut.

 
Well I assume the overrun is to stop buildup of heat (hot spotting) in the heat exchanger, the overrun prevents this, I don't think a bypass will be any good for that. There is always a pump live in the boiler if it requires overrun.

 
The overrun is something to do with the heat exchanger, the plumber mentioned this and implied it was a new reg, whether that's true or not, I don't know.

Thanks for the input guys, I'll be taking a look at the boiler terminals and instructions in the morning, hopefully its a case of the plumber getting his wires crossed!

 
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If there is no way to allow overrun from the boiler, which I doubt, however, domestic heating circuits are not things I "do" TBH!

You can always take a permanent live to a point local to the pump, and use the N&E for the pump, along with the switched live & the perm live to run an off delay timer, which would give you what you need.

 
The boiler will take care of this, you just need to make sure you wire the PUMP from the pump terminals on the boiler.

 
sparkytim said:
The boiler will take care of this, you just need to make sure you wire the PUMP from the pump terminals on the boiler.
Click to expand...
But my earlier point was, unless there's an automatic bypass valve somewhere, then said pump driven from the boiler, may just be pumping into a stop end if all the control valves are shut due to no demand.

 
But I think with a Y-Plan there must be a by-pass with stop tap which is just cranked open usually in the airing cupboard after pump before 3 Port to return.

 
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you will have to run another cable unless an existing core is not used im afraid

 
Yes ive had this before where the existing boiler was replaced Y plan control wiring and a separate cable had to be installed from the boiler to the pump. in the base of the boiler was a removable terminal block kinda like a big black plug with terminals  for boiler supply LN pump LN and switch terminals for the control circuit 

can remember the name of the boiler now

 
I haven't read all the comments on this post, so I may be repeating what someone has already said.

Pump overrun was introduced with the advent of low water content boilers. If the boiler and pump were switched off at the same time by the control system, residual heat in the heat exchanger would cause the small amount of water to flash to steam. A changeover stat was fitted in the heat exchanger to switch control of the pump from the control system, to the boiler overrun circuit. That is why a permanent live from the boiler is needed. The heat was dissipated by the pump action and when the exchanger temperature normalised, the overrun stat passed control back to the control system.

I haven't been involved in control systems for years, although I am a Honeywell trained Controls Engineer. I started with Honeywell in 1964 in their Sheffield Office, where all the "Sundial Systems" were first developed. Before the number-to-number wiring system was developed, I used to send customised wiring diagrams to hundreds of installers around the UK, showing how to wire a particular control system to a particular boiler and usually a separate time clock. My library of wiring diagrams was used to develop the number-to-number system used today.

I was especially involved in diverter valves, with the "W" Plan (V4044) and later the "Y" Plan (V4073). The best system IMHP was the "S" plan, especially when we switched from the V6057 valve to the V4043 spring return one. The older guys may remember that the original "Y" Plans had a plug-in relay on the side of the valve and it needed 6 control wires to operate. In 1972, I emigrated to Canada and worked for Honeywell there, where all these valves were manufactured. Because of my extensive involvement in the UK on the application of their products, I was asked to a meeting with their design team, including the Design Engineer of the V4073 mid-position valve. He was under the impression that, when there was no call for heating and hot water, the valve must return to the mechanically open position of DHW. That's why he had incorporated the relay. I am sure you know that it doesn't matter where the valve settles when de-energised, since there will always be at least one water circuit open. He checked with UK to see if I was correct and then redesigned the internal wiring of the valve, to what it is today.

The "S" Plan closes heating and DHW circuits when there is no demand, so a pump overrun needed to dump surplus heat somewhere. This was usually a towel rail in the bathroom or an adjustable flow bypass valve.

As you may have gathered, I am an old sod, reminiscing about the "old days".

SBS Dave

 
Found this photo in the loft yesterday.

Taken in 1968, when I worked for Honeywell in Sheffield. I was 27 years old at the time.

I was the Inside Sales Engineer and Flame Safeguard Specialist. That's me at the back, in pinstripes !!

I had just built the "N" Plan Panel, shown, which was the low-volt stat version of the "W" Plan.

It was taken for a Publicity shot and for an article in a Trade Magazine.

Four years later, I emigrated to Canada, as mentioned in an earlier post, getting involved in the "Y" Plan, which many of you are very familiar with.

SBS Dave

IMG_1464.JPG

 
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