Testing 6 miniature relays removed from a PCB - Page 1
Forum section: electronics / beginners

author: daveh
author_rank: Newbie
timestamp: July 18, 2013, 09:12:42 pm
content: Hi,1st time poster on here and looking for a bit of guidance.The hot water side of our boiler is not firing up at all, but the central heating side works ok.Having replaced the hot water tap flow sensor with a new one. I've come to the conclusion that the problem is somewhere on the boilers PCB.I've removed the PCB from the boiler and had a very close look at with a magnifying glass, but I can't see any dry joints, burnt out components or broken tracks.A new PCB board will cost me £150, so I am very keen to try to fix it myself and hopefully learn something along the way.I know a tiny bit about electronics, so I am guessing that the most likely components to fail on this PCB would 1 or more of the 6 miniature power relays. Simply because I know relays have moving parts in them. Does this sound plausible?The 6 relays are all the same, and have V23061-A1005-A302 written on them.I've found a datasheet for them herehttp://www.mouser.com/ds/2/418/NG_DS_MSR_0611-110552.pdfThe datasheet says they are MSR relays, but I have no idea what MSR actually stands for, and the datasheet doesn't say either.I am fine with de-soldering them from the PCB with my soldering iron and a bit of braid, but I am stuck with how to actually test them.They are rated as 12 volts. So I guess this means that if 12 volts is applied across pins A1 and A2 it closes the circuit on pins 11 and 14?I have a multi-meter, a breadboard and a few resistors (from when I dabbled with learning electronics many years ago). I want to build a simple circuit on the bread board that will test each relay 1 at a time, but I haven't got a clue where to start really or is there another much simpler way to test them without building a circuit? From reading the datasheet, I'm guessing the first test I should do is check that there is 652 ohms of resistance across pins A1 and A2.Thanks in advance.

author: madires
author_rank: Super Contributor
timestamp: July 18, 2013, 09:42:22 pm
content: Add a freewheeling diode parallel to A1 and A2. If you connect A2 to ground of your PSU the anode should go to A2 and the cathode to A1. Then connect A1 to +12V of your PSU and check if you hear the "click". After that check the switched contacts with your DMM. Do they open and close as expected? Sometimes the contacts "bake" together and you'll hear the click but nothing happens. In that case you could tap the relay with the handle of a screwdriver to loosen the contacts. If that doesn't help you'll have to replace the bad relay.

author: daveh
author_rank: Newbie
timestamp: July 18, 2013, 11:24:22 pm
content: Thanks for your reply madires. I've been doing a bit of googling and reading about freewheeling (or Flyback) diodes.Will the common 1N4007 diode be ok for this testing?

author: Rerouter
author_rank: Super Contributor
timestamp: July 19, 2013, 03:30:23 am
content: yes, its more than sufficient,

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 19, 2013, 08:04:52 am
content: Burnt contacts are a common fault on stuff like this - hard to see on a sealed relay but you can measure resistance of closed contacts.Tapping the relay can often be enough to make it connect, as a diagnostic aid.Assuming it's a fan-flued boiler, is the fan starting? If not, trace the wiring back to find which relay switches it.

author: daveh
author_rank: Newbie
timestamp: July 19, 2013, 10:41:02 am
content: Quote from: mikeselectricstuff on July 19, 2013, 08:04:52 amThanks for replying.Yes, it's a fan-flued boiler, but I don't know to be honest. The boiler works in central heating mode, so I'm guessing the fan must be working from that. All I really know for sure, is that it's not providing hot water.I know from fixing cars, that relays (or anything with moving parts) is usually the first place to look when you get electrical problems.The boiler should spring into life when something called a flow sensor(turbine) detects that a hot water tap has been opened. I've changed that sensor already, but it made no difference. I suppose it's possible that I could have bought a faulty flow sensor, but I don't think so, because on the hot water side of things, there are 2 modes. The first mode is called economy mode and the other mode is called comfort mode. In comfort mode the boiler should fire up occasionally for a few seconds (regardless of whether you turn on a hot water tap or not) to heat up small quantity of water, so that you always have totally instant hot water. In economy mode when you turn the hot tap you have to wait about 10 seconds before the water starts to heat up. We always used economy mode (to save on the gas bill), but as a test, I've put the boiler into comfort mode and it isn't firing up any more. There something very high up the chain of events wrong here. Looking as the circuit board there’s lots of small surface mounted components and IC's. I wouldn't have a clue how to go about testing those.All I think I can do is remove these relays 1 at a time, test them, and solder them back on the board. If none of them are faulty, I will have to bite the bullet and buy a new PCB.

author: Towger
author_rank: Super Contributor
timestamp: July 19, 2013, 10:45:30 am
content: My experience with boiler PCBs is the quality of workmanship is crap and they are exposed to high temperature with wide changes. As you use '£' I assume you are in the UK, so I am talking Potterton and Glow-worm etc.I assume it is through hole, so I put my money on a dry joint, so take out the soldering iron and resolder the whole board. Even if it look fine at first, when you go through each joint one at a time, you may see the problem.

author: daveh
author_rank: Newbie
timestamp: July 19, 2013, 12:30:25 pm
content: Quote from: Towger on July 19, 2013, 10:45:30 amYes, I'm in the UK (I've just updated my profile, so it shows now). The boiler is a Halstead CBX32.Thanks for the tip regarding resoldering the whole board. I will give it a try the best I can, but unfortunately the board is dual layered, and about 80% of the components are those tiny surface mounted things. I think I might find it beyond my capabilities to re-do all those tiny joints.

author: 807
author_rank: Frequent Contributor
timestamp: July 21, 2013, 11:44:20 am
content: Quote from: daveh on July 19, 2013, 12:30:25 pmAs you say, the board is mainly surface mount, so you could do more harm than good trying to reflow the joints.Did you ever try running the hot water tap while the central heating was also on?I don't know anything about boilers, but my Vaillant combi boiler has also suffered a few times in the past with no hot water, but central heating working OK. If I turned up the thermostat to fire up the central heating, I could then get hot water.On every occasion it was down to a faulty diverter valve. I don't know if all combi boilers work in the same way, but if your hot water also worked only while the central heating was on, then it could be down to the diverter valve.

author: daveh
author_rank: Newbie
timestamp: July 21, 2013, 01:56:10 pm
content: Quote from: 807 on July 21, 2013, 11:44:20 amThanks for replying.Yes, I've tried the scenario you describe. If the central heating is running and you turn on a hot water tap, the diverter valve should switch the boiler into hot water mode (hot water takes priority), but it doesn't. The central heating just stays on and the hot water tap continues to run cold and the diverter valve stays in the central heating position. This was reason why I initially thought that hot tap flow turbine(sensor) was faulty.PS. I am convinced the diverter valve motor is not faulty, because if I switch off the central heating and wait a couple of minutes, it moves back to hot water (default) position itself. Then if you switch the central heating back on the diverter valve moves back to the central heating position.Basically the hot water side of the boiler is totally dead and I haven't found any way of getting it to come on.

author: G7PSK
author_rank: Super Contributor
timestamp: October 24, 2013, 07:44:06 am
content: My father had a similar problem with his boiler which was also a combi boiler, the fault was no hot water but the central heating side worked in the end he called out a service man, the fault limescale in the hot water side.

author: Kryoclasm
author_rank: Regular Contributor
timestamp: October 24, 2013, 09:59:08 am
content: In my experience as a boiler technician, those control relays like the ones you have are very bullet proof. You can check if they are working just by putting your finger on the top of it, you will feel it activate.I may of missed it, but is your boiler gas or electrically heated?Troubleshooting: start with this first if you haven't already...Gas boilers won't fire up if the pilot system has tripped off either due to an interruption of gas at some point or if it over heated. (an over temp condition needs to be properly addressed)Electric boilers use a heating element, I'd make sure the circuit breaker hasn't tripped (bad heater element). In the UK are those 220V or 440V?Anyway, those heaters also have a large 2 or 3 phasecontactor(big relay) that will close when the control board sends the signal to turn on.The next likely area of problems are the signals to the small control relays, not necessarily the relays themselves.Really helps to have a good understanding of the control system or have a good wiring diagram to do good troubleshooting.If you hit a brick wall, I'd suggest getting a home heating technician to look at it.Good Luck! Hope you can find the problem.

author: tsmith35
author_rank: Frequent Contributor
timestamp: October 24, 2013, 11:34:27 am
content: Quote from: daveh on July 18, 2013, 09:12:42 pmWhat is the brand and model number of your heating unit?