Boiler not firing up

[Jever]

Hi,

My house is heated by a Myson Velaire oil fuelled boiler (about 30 years old). About a year ago, I got a plumber to come and change the system so that we have a direct pressure feed with a new Unicyl water tank and a Honeywell ST9400C control system to run it all.

Things have worked quite well since then, but I noticed the other morning that it wasn't making the usual sounds when then system comes on in the morning. There's usually the sound of water moving around in the pipes as the boiler comes on to heat the water.

The water continued to be hot, so I didn't worry about it. However, what appears to be happening is that the water is being heated by the electric element in the tank (potentially expensive?), so that the boiler doesn't need to fire up. The boiler's light is still on, it did fire up briefly when I switched the whole system off and back on again, but now it sounds as though the electric element in the cylinder has taken over again (it makes a quiet humming sound).

My initial reaction was to call the plumber, as I've no idea why the boiler is no longer doing as it should, but then I don't want to call him for something stupid.

Are there a few simple checks I could do before calling the plumber? What is it that causes the system to switch to electric instead of oil?

Would appreciate any help you can offer.

Regards

Jever

 

[Agile]

Why do you have the electric heater turned on at all?

 

[Jever]

Hi,

That's the bit that puzzles me. In the airing cubpoard, there's a switch that looks like a light switch, which I assume is what switches the electric element on or off. It's always in the 'off' position.

Yet when I look at the tank (see picture attached), the red light for the temperature control is on, regardless of whether the timer setting for hot water means water is being heated or not. It also makes a sound like when you've just turned the kettle on, but quieter, which is what leads me to conclude that the electric element is on. You could assume that the element switch is wired wrongly, but why would this start happening after a year, having worked properly before?

Should I remove the casing to the element and see if it has power supplied to it?

 

[gassymark]

That type of stat incorporates a anti legonella program and may be faulty and raising the temp above boiler stat set point.
Mark

 

[Jever]

Hi,

I've investigated a bit further and switched the system off overnight. When I turned it back on, the boiler fired up and worked as usual.

I suspect the reason it wasn't firing up before (or making so much noise on start up) was that I had turned the temparature down on the tank and so there wasn't the need to heat the water as much.

I've also check the electric element with a current detector. There's current when the switch in the airing cupboard is on and none when it's off - so no problem there.

Having listened more closely, the 'kettle-like' sound is actually the sound of the electric pump working non-stop. If the system's on, it's pumping. I don't understand this, as it's supposed to be a mains fed system. Nonetheless, regardless of whether the heating or the water are swithed on or off, the pump's running. I would have thought it would only be needed for the central heating.

Is this normal for a mains fed system?

Regards

Jever

 

[Agile]

The circulating pump is needed whenever the boiler is providing heat to the CH or HW or both!

Tony

 

[Jever]

Ah, ok thanks, I didn't realise that.

But surely it should switch off if both the hot water and the central heating are switched off (i.e. both are outside of their switched on times)?

They're both supposed to switch off at 10 pm, yet when I go to bed (after 10 pm) I can still hear it whirring away. It's definitely still pumping.

Regards

Jever