megaflo hot water system keeps cutting out

[agentgonzo]

I've got a problem with my central heating. I've got a megaflo unvented system with an indirect gas boiler.

When I turn on the heating at the boiler controls, the boiler only stays on for a couple of minutes before cutting out. Here's what happens in detail.

We ran out of hot water.
I turned the boilers control for hot water on to constant and the boiler fired up.
It ran for a few minutes, then clicked off as if the tank was hot enough (it wasn't).
It would then wait maybe five minutes, then the boiler would start up again, stay on for a minute and then turn off again. Then do it again, and again. I now have to keep it 'on' all day just to have enough hot water for a shower as it heats it up in tiny bursts.

I've checked that there is hot water being circulated to the megaflo cylinder - I had my hands on the inflow and outflow pipes for the heating circuit on the cylinder. When boiler is off, they are warm. As soon as the boiler starts, one pipe (in) goes hot and the other goes cold. Then they gradually equalise. I measured this with a laser thermometer and the in pipe was 32 degrees and the out pipe was 30 when it cut out.

The thermostat on the megaflo is set to about 65. If I pull this way down I can hear it clicking as I rotate it to trigger the heating on/off and the water coming out of the tank is about 25 degrees. So the tank isn't hot and the thermostat appears to work OK.

I can hear a motorised valve in the megaflo shutting before the boiler's pump motor stops and the gas turns off, so it seems that the megaflo shuts its valve and the boiler responds to this rather than the other way around.

To my eyes, it looks as if this motorised valve is shutting when it shouldnt, but I don't know why.

Can anyone give me any guidance please?

This system was already installed in the house when I bought it a couple of years ago so don't have and details of when it was services etc (if ever). Boiler serviced last year. Central heating is fine.

 

[jeff the gasman]

Sounds like a faulty motorised valve but as it's part of a megaflow safety system you should get a G3 plumber in.
Jeff

 

[agentgonzo]

Thanks Jeff.

When you say it's a faulty motorised valve, do you mean the motor itself, or the valve, or whatever it is that controls it (or does it control itself?). The reason that I ask is that it seems to open/close (I can hear it whir when it opens and feel the hot water flow through the system and the same when it closes) so surely the motor and valve work and it's whatever is instructing it to open/close that could be at fault? Or does the motorised valve decide by itself when to open/close?

Thanks for your help. I'll get a plumber (unless it's a simple fix that I can do) but want to be as specific as possible before finding one so I don't get taken for a mug and fleeced.

I had a look this morning and it's a Sunvic 2-port motorised valve in the airing cupboard by the megaflo cylinder.

 

[agentgonzo]

I just had another thought. Even though it's heated from the boiler, it has an immersion heater in it. I am thinking that if I turn the boiler off and turn the immersion heater on, then if it just heats the hot water up continuously then it means that the thermostat is OK (and the fault lies with the motorised valve). If it turns the element on/off/on/off about the same cycle as with the boiler, it would mean that the thermostat is faulty (as the motorised valve isn't used at all).

Does that sound like it would help to diagnose the problem or would it be a waste of time? I can check when I get home this evening.

 

[HMac]

Hello Agentgonzo
I seem to have something similar with quite cold water from the coil outflow when the hot inflow starts and intermittent boiler firing. Did you get to the bottom of the problem and solve your problem?