Central Heating Buzzing - What is this component ?

TalkTalkBoy

Hi,

A box which is connected to my central heating pump is making a loud buzzing noise. I've tried searching the part number on the internet but can't find anything. Any ideas on what i need to replace this ?



P.s there is a wire diconnected which came out when i took the photo but it is reconnected now but still makes a noise

Belnahua

Could it be an electronic valve?

TalkTalkBoy

Bot usre but it needs replacing because it's so loud its keeping me awake at night

andrew-b

There's a step-down transformer stepping down from mains AC voltage to 48Volts DC (the little black box part at top right) so that would be most likely what's making the buzzing noise. There's a motorola chip of some sort (perhaps an op amp?) a few resistors and capacators and a variable resistor with thumbwheel at bottom left. My guess is it's a speed controller for the pump. If you turn the wheel from max to min what happens?

Andy

mikey72

It's a timer.
The black box is a relay, and the chip is a MC14541, programmable timer. The relay is probably buzzing, but have you a photo of what the box is attached to?

thescouselander

Another vote here for the relay. Should be easy enough to change the component and its probably not expensive (if you can find one). I'd have a look in the Maplin or RS catalogue to see if they have got something that will do.

If you search on the net for OMRON G5LE-112P-PS it brings up a few results too.

andrew-b

Ahh yes your right... i couldn't read the label on the chip. Misread it as MG14541..so google didn't help me.

They said connected to central heating pump so maybe it's an overrun timer to keep the pump running for a bit longer? Seems a strange setup to me if it is - perhaps fairly old?

Andy

TalkTalkBoy

Can i not just remove this if it's an overrun timer ?

It connects into a junction box which is just below it and into this all the cables from the pump and boiler go into.

I've already tried moving it from Min to Max but the loud buzzing stays exactly the same.

27col

The pink coloured resistor seems to be getting hot and damaging the circuit board.

mikey72

The resistor is probably dropping the 240v down to 48v, it could degrade with time, or the 5 volt zener could have gone. Or it could be the relay. To answer the previous posting if it's an overrun timer it may be keeping the pump running until the boiler has cooled down, but without being there it could be a dozen other things as well. I'd hate to guess.

k2joom

The black item, top right is a relay, Omron G5LE-112P-PS-3 SPDT 5A 12VDC.
Datasheet available from here, but its Japanese. www dot fa.omron.co.jp/data_pdf/closed/prdn-2795.pdf
This version is the one on the left.

Basically, its an electro-mechanical switch. When a voltage is applied to the input, the output will switch. you can see pins 3 and 4 is the switch section.

There are two main types of relay NO (normally open) and NC (normally closed) this relates to the output state, it gets complicated from here on in, so I will hold off.

There is a guy on Ebay selling them, current link is: cgi.ebay.com/20-OMRON-G5LE-112P-PS-24VDC-SHIPPING-DEPEND-QUANTITY-/270633841310

In the case of it buzzing, it could be that the switch inside is sticking, or the control circuit is failing and causing extra pulses to the relay.

The resistor, brown component with burnt around the board, it is normal to see some discolouration. This is due to the resistor dropping a lot of voltage across it, too much tech speak. This is typically caused by poor circuit design, low grade component or a sign of something failing.

If your not technical, then it might be best to replace the board if you can get it from the boiler manufacturer.
I would certainly advise to use caution when working in the boiler, PLEASE make sure you turn off the power to the boiler, as there will be mains voltage in there.

Simon