Apollo 30/50B randomly switching off pump when still heating

[gillsfan]

Hi guys

I've been a regular reader of these forums over the years and always found the advice sound - it's extended the life of my boiler, for sure! So, I think I might have one to test you here:

Thorn Apollo 30/50B, open vented system. Bolier in kitchen, upstairs in airing cupboard is hot water tank, 3 way valve and pump. Pump replaced about 2 years ago with a Grundfos - like for like. Hi and lo stats and thermocouple have all been replaced in the last 3 years at various times. Expansion tank in loft - works OK as I've had to lock it off and use it to fill the system when fernoxing. Basic working is fine - all rads heat up OK, no apparent airlocks, 3 way seems to work fine as it will heat up just hot water when I switch it over. System has been fernoxed twice in the last 3 years (once as a maintenance thing, then last year when the boiler kettled after the hi stat went) - boiler is probably about 17 years old. Basically working OK apart from an issue which has been happening for about 4 months. Started off being a once in a blue moon thing, has gradually got worse. Now, there are 2 separate issues but they may be related as they seemed to start happening at the same time, and there is a certain amount of crossover as well.

1) On the lo stat setting, when on central heating, intermittently the pump will stop running whilst still heating the water. This will kettle the boiler and then the pump seems to spring back into life again, normally in about a minute or so. Carries on working OK and then it may happen a few times more in the 5 hours I normally have it on in the evening at the mo. This issue seems to be getting worse just recently.

2) On the hi stat setting, everything heats up well and then randomly at some point, the system trips the house mains supply, the boiler switches off, punp stops etc, but the boiler pilot seems to stay lit as once I reset the trip, the boiler comes back on (I'm assuming this is the thermocouple doing it's job but I thought that by tripping the mains it should kill the boiler too? Mayne I'm getting confused!) however you can pretty much guarantee that a few minutes later it will trip the supply again. Switching to lo stat seems to reduce this problem drastically.

If I leave the house with the heating switched off for a while (i.e. when I was away for 2 weeks recently) then problem 2) will occur on the lo stat setting too. Once I've reset the mains a few times and the boiler has been on for a while then this stops on lo stat but it is very consistent on hi stat. It has popped the mains on the lo stat once in the last 3 weeks, but I tested the hi stat today and within half an hour everything went off again.

PLUS I have heard the pump stop running as in problem 1) when on the hi stat setting as well. Luckily, the boiler wasn't heating at the time, it was inbetween heats, so all was OK - again the pump started again after about a minute. Very strange!

I have noticed that when 1) is occurring, I get a lot of interference on the TV screen, so I'm wondering if there's a possible issue with something switching inside the boiler, hence the spiking on the mains on the TV which might also be a symptom of problem 2) which results in a sufficient spike to trip the mains (mind you, my RCD is VERY sensitive - it has been known to trip the house when I switch on my PC at the mains!)

I know there's a pump overrun stat on this unit, but I though that it's only purpose is to keep the pump running for 5-15 mins to cool the water down a bit after the timer switches off. Does this get involved in the normal running of the unit, and more importantly could it be a possible cause of the issue?

I appreciate the boiler is knocking on a bit and that you may recommend a replacement condenser boiler, however there seems to be a major difference of opinion on this forum as to what's a good one! To me that says there isn't one out there that stands out as a quality unit - let me know if I've got the wrong end of the stick there! I'd rather not replace the Apollo if I can fix it myself, as to be honest apart from standard wear and tear things going wrong with it (up to this point!) it's been a solid and reliable unit, and having done a lot of maintenance on it myself, I've got to know the unit quite well, so I'm happy to try anything you guys suggest and, within reason, quite happy to replace parts. Plus I am a great believer in keeping things simple - Apollo is simple, condenser boiler sounds complicated

I hope I've covered everything there - if not please ask. Any help will be, as ever from this forum, greatly appreciated.

Cheers

Mark

 

[meldrew's_mate]

Mark, nice detail here, I'll try to answer as much as I can.

1. Pump over-run function comes from either a thermal changeover switch, or a changeover relay on the PCB, and switches permanent live supply to the pump whenever the boiler temp is over the notional switch setting. This is not user adjustable, but suggests that if this switch contact is breaking down or loose on the pcb the pump may stop.

This explains why the low setting was more reliable than the high setting until recently when the contact deteriorated.

The arcing of the contact may well interfere with the TV reception by generation of RF noise, though it will be much more prevailent on Radio 4!

My recommendation is to check all the soldered joints on the pcb around the relays, re-solder as necessary.

2. RCD tripping is caused by leakage to earth from an insulator breaking down. Suspect the pump (I know it's nearly new, but....) and the fan if it is the fanned flue model, though it could just as easily be induced by the switching noise coupled with your very sensitive RCD.

A competant electrician will be able to check your 30mA RCD by injecting 10mA and 20mA to earth, and looking for other sources of earth leakage on other circuits. Remember, if you have old wiring with a constant leakage of 20mA to earth it only takes a few more from your heating cct to trip it.

Went to quote on replacing a Thorn Apollo Fanfare today, fanned flue version. The boiler wasn't working properly, flame kept extinguishing. It turned out the builder (of the new extension) had built the new wall to within 3" of the flue's discharge, leading to dilution of the oxygen content of the intake air and flame lift-off. The boiler was going start-stop every few seconds and "taking ages to heat the water". The builder had not "interfered with the boiler" so didn't think he was in the wrong. The flue CO levels must have been enormous. And the customer said he thought it would improve when they got the windows in on Monday.
Left to his own devices he would have sealed the flue discharge into the house, putting everyone's life at risk who slept there.)

One final point, you must realise that working on the gas parts or flue of your own boiler, unless CORGI registered, is illegal; proceed at your own risk (to you and your family/visitors - see previous paragraph)

 

[gillsfan]

M-M - many thanks for the advice, as sound as ever from here. I hear what you're saying about messing with the gas elements of the boiler - I would always get someone in if that needed fixing, and I have a CO meter in the kitchen, just in case, as it is an old boiler and I have no idea what, if any, work was performed on it before I moved in 5 years ago. But soldering and electrics - that I can do so I will check out the PCB and get my trusty soldering iron out today.

Appreciate the time you spent posting that reply!

Cheers
Mark

 

[John.B]

Apollo 30/50B. Pump stat faulty,located inside boiler to the rear on bottom right hand side.
Three wires to it red, yellow and brown. No pcb on 30/50 B. Switch off power before replacing as one wire is permanently live.

 

[gillsfan]

Cheers for that - it's the only stat I haven't replaced on the boiler so I will give that a go!