uNDERSTANDING THE PUMP OVER-RUN

[nigelm]

My boiler as a switched live (turns the boiler on) and a live from the boiler to the pump.

I am assuming that the live to the pump allows the pump to continue to run for a time after the boiler to stop firing when the return temperature is high. (this being controlled by the boiler).

When however the room stat operates the live to the boiler is switched off, the boiler and pump stop imediatly.

Does this sound correct?

 

[D_Hailsham]

Make and Model of boiler, please.

 

[BertieGas]

As a rule there is a permanent live to the boiler, a switched live to the boiler, and a live out to the pump. This seems to confuse most people. I am currently rewiring the work of a heating engineer and an electrician who seem to be a bit Laurel and Hardy at pump over runs.

 

[gasmick2]

the normal practice was to supply a permenent live to the boiler and a switched live to the boiler from the programmer, the pump is wired into the boiler pump connections on the boiler connection strip, the ranco stats had a changeover built in so leaving the pump running for 3 mins after the stats have swithed off and after the proggrammer has turned off it then switches back to the normal operating mode ready for the next call for heat
I have been to loads of Y plans where the pump was wired up with the boiler connections direct from the orange wire from the diverter valves
no wonder the heat exchangers got corroded up as the latent heat could not be dissapated away for cooling

 

[Paul Barker]

Yes it's a major misgiving in the idustry today that installers and electricians don't wire up pump overrun boilers properly. It's all been said above how to do it.

For any regular boiler like the Alpha 13r some biasis etc assume it needs a permanent live.

The problem is that many of these replace cast iron boilers which didn't require pump overrun so there simply weren't enough wires in the old install.

You would have thought the advent of part P would have improved quality of electrical trade work on central heating. But no what has happened is people like me who paid the tousands to comply have been driven out on grounds of resultant low profitability, and the elctrical work on heating remains as apauling as it alwasy was. and as predicted by many nobody polices part p.

Just like with corgi registration the people who are policed are the ones who have paid out for training equipment insurance and membership.

Will somebody in government please wake up to the fact that it is the unregistered who are the problem, scoop up all your nic and napit and corgi inspectors and send them out to find the work being done by the unregistered instead. Those who are registered have crossed the hurdles to prove competence more benefit to your socialist state would be achieved protecting the proletariate from those who have not proved competence.

 

[nigelm]

The Boiler is OLD, a Myson Orion.

There is a connection for the pump at the boiler, but as there is no permanent live it would seem that it would not have a proper pump overrun facility.

 

[D_Hailsham]

The Boiler is OLD, a Myson Orion.

A quick look at the wiring diagram in the installation manual at http://www.partsarena.co.uk/baxi/ shows that the Orion does not have a pump overrun. The pump will stop when the room stat has reached temperature.

The wiring diagrams show in the installation manual do not meet current requirements as no there is no interlock. The time switch turns the boiler on/off, the room stat starts/stops the pump but the boiler will continue running until the boiler thermostat turns the boiler off. An interlock will turn the boiler off when the room stat is satisfied.

 

[nigelm]

The boiler as been wired so that it turns on (live feed) when either of the two port valves are open, the pump runs at the same time. effectively the boiler does turn off on the cylinder thermostat and the room thermostat.

 

[D_Hailsham]

The boiler as been wired so that it turns on (live feed) when either of the two port valves are open, the pump runs at the same time. effectively the boiler does turn off on the cylinder thermostat and the room thermostat.

OK you do have an interlock

You don't say if you have the B version or the Si version of the Orion. The main difference is that the Si has a fan and this needs a permanent power supply to the boiler. So, if there is no power at all to the boiler when the valves are closed, the fan will not be able to run when the boiler is off, which is essential. (The fan need to run, even when the boiler is off, to clear out the fumes from the permanent pilot light.)