boiler (pump constantly running)

30 Jan 2004
Reaction score
United Kingdom
I have just had my boiler moved to another part of the house. I noticed last week that pump was running but heating controls were off. To switch pump off I had to switch the electric supply to boiler off. Bought a new pcb and fitted it and seemed all ok. Noticed recently that fault has returned. Any ideas? Boiler is a baxi solo 3 pfl 70 and is controlled by two port valves for heating and hot water. There is also a flow switch that has been fitted in series with pressure switch.
Sponsored Links
With so many changes and system modifications I would be wary of saying much without seeing it !

I think that model is normally its wired so the PCB controls the pump.

Perhaps the pump is slightly faulty and has damaged the relay on the PCB.

Faulty zone valve?

I had this problem recently on an s-plan system and traced it to the zone valves.
Sponsored Links
after dropping power to boiler all is ok when power is switched back on. if relay on pcb was faulty surely pump would start up again on its own.
definitely not zone valves pump is controlled through pcb which is controlled by valves which also bring on boiler
there are 4 connections going to boiler, neutral, earth, switched live and permanent live.
there should also be a pump live connected to the boiler
time clock opens valves which then switch power to switched live of boiler. permanent live comes straight from spur unit which also powers time clock. these four conductors (switched live, permanent live, earth and neutral) all connect into pcb. pump connections live, neutral and earth also connect to pcb they are all clearly marked and wired up correctly
there are 4 connections going to boiler, neutral, earth, switched live and permanent live.

In that case how does the pump connect to the PCB when there are only four connections which are used for other functions?

this is the wiring , as per MI. Is yours like this?
if there is no power to switch live when demand for both HW and CH is cut AND the pump runs indefinitely then I think your PCB is ***ed
ithink that also but it is a replacement pcb and dont know what is causing it to **** up. Might have to get in touch with baxi £££££
replacement pcb was faulty. managed to get it exchanged. all now working ok. many thanks to agile, gasright, kevindgas and twgas for your advice

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links