Megaflo heating system problem

[fgkynaston]

Hi I have a Megaflo indirect unvented system attached to an Ideal Classic bolier. The system is 3 years old. I have noticed in the last couple of days that the pump seems to be on permanently. I swithched the HW and CH off at the control box and ran all the hot water away, but the pump stays on and the pipes either side of it and the pump itself are very hot. Is this correct or is there something wrong. we have never heard this noise on constantly before. Any advice greatly appreciated.

[Ron Lowe]

No, something is wrong. Without knowing the exact layout of the system, it's hard to be specific.

The basic layout I'd expect to see is: A controller ( timer ) of some sort which gives a live output at certain times of day ( or not, if you select OFF. ). This then also goes through a thermostat ( room stat for CH, tank stat for HW ). The final output of this ( timer says ON, + stat says ON ) opens a zone valve. Once the zone valve is open, a microswitch trips which starts the boiler / pump.

The only way to fault-find is to understand the wiring of the system, and to use a multimeter to fault-find.

If the boiler / pump is running when the controller is at ALL STOP, then either: The controller is bad ( live output when set to off ); A zone valve is bad ( jammed mechanism / microswitch, fed from perm live ); Boiler PCB fault ( if boiler PCB controls pump also ).

If you didn't understand a word of the above, you need to get someone who does.

[Chas]

If you didn't understand a word of the above then you need to get someone who knows how to explain things in a way that makes sense.

[The Natural Philosopher]

Sounds like stuck motorised valve.

In general the controller feeds the 'stats, which feed the motorised valves. These have microswitches on them so that they have to be open before the boiler and pump fires up.

[fgkynaston]

Hi Ron, thanks for quick response. I have looked at system and tried another couple of things. The pump in airing cupboard next to megaflow cylinder has a 3 postion switch which seems to control flow rate with settings I, II, or III. It was on the higest III, but I did change it and it reduced the noise, but still very hot . I also took the large silver screw out of the centre to bleed it, a small amount of water came out and I could see the impellor turning inside. Wasn't sure if that should actually be full of water, hence so hot. Also on the primary flow line which the pump is teed off. there is a danfoss HPV 22 valve with an Auto and Manual postion before pump and a Honeywell Valve with Auto and manual after the pump. If I switch either or both of these to Manual the noise from the pump stops. Can this do any harm. if I put the honeywell one to manual it appears to allow the feed to the radiators which then get hot. One other important thing I noticed this morning that with the Controller/ timer.Set to off for HW and CH, the pump was still running and it and and the pipe in and out of it were very hot and we had very hot water. and for some reason I noticed that the boiler had come on undemanded for a short time. does this make things any clearer. Thanks very much for any advice. bit concerned as called 3 plumbers and no one interested at weekend.