Myson Apollo boiler trips electricity/power

[angry_gekko]

I have a Myson Apollo 30/50 boiler, fitted with a manual programme ring. The programmer has the choice of Timed/Off/Continuous, HW/HW+CH and Low/O/High thermostat. The system is vented (there is an expansion/feed tank in the loft) and configured as a Y plan. The pump is a Grundfos 16/50, the three port valve is controlled by a Honeywell head and I believe the room thermostat is a bi-metallic strip type. The house has four bedrooms, and contains 10 radiators.

The system worked fine last winter and has also been happily providing ‘HW only’ all summer. However, as soon as the days started to become cooler and we switched the boiler to HW+CH, the following problem has arisen:

The boiler will come on and the system will heat up for about 15-20 minutes after which the main power circuit breaker will trip and we loose electricity to the whole house. Restarting the boiler on either HW or HW+CH will cause the power to cut out again very shortly (sometimes almost instantly sometimes a few minutes). The system does however appear to be able to provide ‘HW only’ when started from cold in the mornings.

Initially we suspected the pump, so I re-wired the pump direct to a plug and ran it from a wall socket for a few hours with no problem. Then we thought that maybe the boiler was overheating, but after a few days of no CH the boiler stopped lighting the main burner when the timer came on – the pump would still run though, and the power would trip after 20min when set to CH+HW, even though the boiler was only being warmed by the pilot.

At this point we called in an engineer. His opinion was that the boiler was ok and that given a service would last a few more years yet. He managed to get the main burner to light without changing any parts (I think he held the gas valve in whilst he flicked the boiler on?) He then tested the reactions of the 3 port valve to various boiler/thermostat settings and was happy. He suggested that the pump may be overheating, damaging its coils and tripping the power (the pump did get hot quite quickly, although no hotter than the surrounding pipework). He replaced the pump (with a Grundfos 15/50) however this has not solved the problem and the power still tripped when trying to heat the CH.

The power trips seem to occur regardless of whether the room thermostat is set so as to be On/Off, the programmer is set to Timed/Continuous or the boiler thermostat is set to Low/High (although I have not yet seen it trip with the thermostat set to 0).

Apologies for the mini essay, but any ideas that I can suggest to the engineer to help solve the problem quickly would be greatly appreciated.

 

[tryitandsee]

If running on hw OK all of the time, have you isolated/disconnected the room thermostat to eliminate this out of the equation.

 

[Agile]

Why did you call someone who was unable to locate the earth leakage fault?

Why not call Tryitandsee and let him find it?

Tony

 

[angry_gekko]

tryitandsee, I haven't isolated the room thermostat, although I have tried running with it set to both above and below ambient temperature. Also, this morning I left the boiler set to HW, removed the 3port valve head and manually twisted the spindle to HW+CH. The power again tripped after 20min - does this remove the room thermostat from the equation?

To isolate the room stat is it just a case of temporarily connecting the two wires?

Agile, I just called a corgi registered engineer, I didnt know what the fault was or whether he would be able fix it. How would you go about tracing an earth leakage fault if this is what you beleive it is?

Thanks for the replies.

 

[tryitandsee]

Interesting problem. It appears to trip after 20mins on Central heating. By manually turning 3 port valve I presume you were avoiding/testing other electrical circuits.

Does the central heating flow return have a thermostat on it, my thoughts being after 20mins it activates-tripping circuit.

Agile, I'm only a DIY'er as my forum name suggests. No problem with sharing ideas to help solve/eliminate annoying dilemmas.

 

[angry_gekko]

That is correct, since the system seemed to work when set to HW I was trying to isolate the 3 port valve motor.

Interesting and frustrating! The fact that it tripped this morning makes me think that it is something over heating: For HW only the boiler doesn't need to be on for too long a period, whereas when I moved the valve manually nothing had changed 'electronically' yet the pump/boiler would have to work harder to heat/pump the greater volume of water.

No external thermostat that I am aware of (unless anyone has any ideas where it may be hidden!). According to the manual the boiler has a thermal cut out on the heat exchanger (but this should cut the pilot and the pilot has remained alight throughout). Also there are high and low thermostats and a pump over-run thermostat.

 

[tryitandsee]

Thinking about it, the central heating sensor (if it has one) is only an on/off switch reacting to heat, so when it switches (after 20mins), is it this that trips the mains, indicating the problem to the circuit board.

Do let us know what is causing this-when you eventually find out.

 

[angry_gekko]

Is a 'central heating sensor' a common feature and if so where would it be located?

I am still wondering whether its just the boiler overheating - the last time it tripped it was incredibly hot to touch, is it possible that the sensor regulating the temperature of the water in the system is cutting the power rather than the main burner?

 

[D_Hailsham]

Let's look at this logically!

The boiler will come on and the system will heat up for about 15-20 minutes after which the main power circuit breaker will trip and we loose electricity to the whole house. Restarting the boiler on either HW or HW+CH will cause the power to cut out again very shortly (sometimes almost instantly sometimes a few minutes). The system does however appear to be able to provide ‘HW only’ when started from cold in the mornings.

1. Have you had any work done on the system over the summer? e.g servicing.

2. What size fuse do you have in feed to central heating? It should only be 3amp. If the main Breaker is going and shutting of the whole house, the chances are that you have the wrong fuse!

Initially we suspected the pump, so I re-wired the pump direct to a plug and ran it from a wall socket for a few hours with no problem.

Do you mean that it ran without tripping the circuit breaker?

If so, then the pump overrun thermostat is faulty.

Then we thought that maybe the boiler was overheating, but after a few days of no CH the boiler stopped lighting the main burner when the timer came on – the pump would still run though, and the power would trip after 20min when set to CH+HW, even though the boiler was only being warmed by the pilot.

How was the pump wired when this happened? to the boiler or on the separate plug?

He replaced the pump (with a Grundfos 15/50) however this has not solved the problem and the power still tripped when trying to heat the CH.

But it is OK on HW only?

The power trips seem to occur regardless of whether the room thermostat is set so as to be On/Off, the programmer is set to Timed/Continuous or the boiler thermostat is set to Low/High (although I have not yet seen it trip with the thermostat set to 0).

If these were the cause you would also have the problem when switched to HW only. The 0 setting on the boiler thermostat is the OFF position, so i'm not surprised you have not seen it trip!!

Does the pump still get very hot?

Why did you call someone who was unable to locate the earth leakage fault?

If it was an earth leakage it would blow immediately, not after 20 minutes. Sounds more like something is drawing too much current when it gets hot.

Also, this morning I left the boiler set to HW, removed the 3port valve head and manually twisted the spindle to HW+CH. The power again tripped after 20min - does this remove the room thermostat from the equation?

The spindle of a 3port valve can stop in three positions: CH only, port A open; mid, ports A and B open; HW only, port B open. Which position do you mean?

Do you have a thermostat on the side of the HW cylinder to control the HW temperature? If so, what happens if you turn it right down? This will move the mid pos valve over to the CH position so the boiler is just running the central heating.

Are you sure that the pump is working? The easy test is to hold a long screwdriver with the sharp end on the body of the pump and the other end pressed against you ear.

As the problem only happens when you switch over from HW to HW and CH, you need to look at what is affected when you do this. I looked up the wiring diagram for an Apollo using Y plan and the only thing affected is the mid position valve.

In HW only the valve has no voltage applied, it is held by a spring so that port B is open and port A closed. The fact that your problem only occurs when you turn on CH suggests that it is something to do with the valve, possibly the motor is overheating.

 

[angry_gekko]

Thanks for such a comprehensive response! I shall do my best...

1. There hasn't been any work done over the summer (I dont think anyone has touched the system for well over a year now).

2. The fuse in the socket controls the boiler is 3amp and I presume this is the only supply of power to the system? (would this fuse go if the system drew more than 3 amps or would the the main circuit breaker cut the power first?)

3. Yes, when run from a seperate plug the pump ran without tripping the power for a good few hours. However, the pump over-run stat does start the pump when heated by a lighter - does that prove if its working or are there any other tests?

4. When the main burner stopped lighting but the power still tripped I believe that the pump was wired back into the sytem (i'm not 100% certain though).

5. Ok, I think my original belief that the trips only occur when the CH is on was wrong. Generally when set to HW only no trips occur - but then normally the HW tank heats up and stops calling for the main burner before 15-20mins is reached.

On two occasions the trips have occured when the whole system is set to provide HW only:

a) when I remove the valve head and manually set to A+B, and
b) this morning with the valve head replaced and everything back to normal, system set to HW and the shower run to use hot water (this caused the boiler to stay lit for 20 minutes trying to heat the HW tank and it tripped hte power)

I therefore think that the fault occurs when the boiler is under heavy load / on for an extended period.

6. The new pump still gets hot, almost as hot as the surrounding pipework (is this normal?)

7. As above, the spindle was set to HW+CH to the best of my judgement (and pipes both side of the tee did get hot)

8. Yes there is a thermostat on the HW tank and turning it down does move the valve to the CH only position. I haven't run the system under this configuration but will do and report back.

9. Pretty sure the pump running. With the original pump I unscrewed the big screw on the front and could feel the spindle turning. The new pump feels the same as the old one (in terms of vibration when on) and the engineer seemed happy that it was running when he installed it.

10. As above, I am not so sure that the problem is directly related to the CH being on anymore.

Thanks again for your help!

 

[D_Hailsham]

Thanks for such a comprehensive response! I shall do my best...

Only another DIYer trying to help!

1. There hasn't been any work done over the summer (I dont think anyone has touched the system for well over a year now).

That eliminates "engineer" problems!

2. The fuse in the socket controls the boiler is 3amp and I presume this is the only supply of power to the system? (would this fuse go if the system drew more than 3 amps or would the the main circuit breaker cut the power first?)

There shouldn't be another fuse, but you never know! Where are the boiler, pump and 3port valve etc physically related? Is there are wiring centre (box with lots of wires going into it)? Or does everything wire back to the boiler?

The 3 amp fuse should blow first but some fuses will take a heavy overcurrent (depends on quality)

3. Yes, when run from a seperate plug the pump ran without tripping the power for a good few hours. However, the pump over-run stat does start the pump when heated by a lighter - does that prove if its working or are there any other tests?

The pump overrun stat is like a two-way switch. When the boiler starts up the switch is in the "cold" position and the pump gets its power via the timeswitch and heating controls. As the boiler heats up the switch moves over to the "hot" position and is fed directly from the mains input to the boiler. When the boiler turns off (time switch or thermostat) the pump will keep running until the boiler has cooled down, the pump stat then reverts to the cold position, but the pump doesn't run as there is no power!

You say that you have a book for the boiler; does it have a wiring diagram? If not, you can find one at:

http://85.189.44.185/Baxi/

You will be asked of you want to download an ActiveX control. It is safe and necessary!

4. When the main burner stopped lighting but the power still tripped I believe that the pump was wired back into the sytem (i'm not 100% certain though).

5. Ok, I think my original belief that the trips only occur when the CH is on was wrong. Generally when set to HW only no trips occur - but then normally the HW tank heats up and stops calling for the main burner before 15-20mins is reached.

On two occasions the trips have occured when the whole system is set to provide HW only:

a) when I remove the valve head and manually set to A+B, and
b) this morning with the valve head replaced and everything back to normal, system set to HW and the shower run to use hot water (this caused the boiler to stay lit for 20 minutes trying to heat the HW tank and it tripped hte power)

I therefore think that the fault occurs when the boiler is under heavy load / on for an extended period.

What make is the 3port valve and which port is HW and which CH?

If the valve is plumbed in as per mfr instructions and the power trips when on HW only the 3port valve can't be the culprit. But, if installed back to front, it could be.

6. The new pump still gets hot, almost as hot as the surrounding pipework (is this normal?)

It is carrying water at the same temperature so I don't see any problem in it getting as hot as the pipes. If it is hotter then I would start to worry as it implies that there is excessive friction!

9. Pretty sure the pump running. With the original pump I unscrewed the big screw on the front and could feel the spindle turning. The new pump feels the same as the old one (in terms of vibration when on) and the engineer seemed happy that it was running when he installed it.

But is the pump doing any work? ie moving any water.

You need to check:

1. 3port valve is the right way round! Radiators on port A; HW tank on port B

2. That the pump runs when the boiler is firing and continues to run afterwards for about 10 minutes. The easiest way to do this is to set the boiler to HW only and turn the tank stat up so it fires and listebn to the pump. After 10 -15 minutes turn the tank stat right down and listen to the pump again. If you don't hear it running both times then the overrun stat is faulty and needs replacing.

 

[angry_gekko]

Right, thanks for the diagrams these are the same drawings that appear in the instructions but that is a useful resource nonetheless.

The pump does run continousely when the boiler fires and the overun stat appears to keep it running for some time afer the burner shuts down.

*** An interesting development! ***

Last week I unscrewed the front of the control panel in order to get a multimeter onto the back of the thermostat switch (the reason being that from there I could measure the resistance of the low stat and thus determine whether the low stat was triggering before or after the power tripped). What actually happened was that the boiler worked exactly as it was supposed to and continued to do so for a number of hours until I screwed the front panel back up!

It seems that the boiler works fine with the front panel hanging down (as it has been for the last week!) but as soon as I replace it the power tripping problem re-occurs. Trouble is, I can see no obvoius reason why this would be the case - there are no bare wires that would be brought into contact with the casing/front panel and I cant understand why it would happen after 15-20 minutes and not as soon as the boiler comes on.

Very grateful for all those that have made suggestions and at least I have a temporary work-around but I would love to finish the job and get the casing back on the boiler!

 

[D_Hailsham]

The pump does run continousely when the boiler fires and the overun stat appears to keep it running for some time afer the burner shuts down.

That eliminates the overrun stat

Last week I unscrewed the front of the control ... What actually happened was that the boiler worked exactly as it was supposed to and continued to do so for a number of hours until I screwed the front panel back up!

Did you check it in all possible settings?
1. HW only
2. HW and CH with HW only (CH stat turned down)
3. HW and CH with CH only (CH stat turned up HW stat down)
4. HW and CH with both (CH stat turned up; HW stat turned up)

This will check the mid position valve in all positions. My reason for asking this is that in an earlier post you said:

5. Ok, I think my original belief that the trips only occur when the CH is on was wrong. Generally when set to HW only no trips occur - but then normally the HW tank heats up and stops calling for the main burner before 15-20mins is reached.

On two occasions the trips have occured when the whole system is set to provide HW only:

a) when I remove the valve head and manually set to A+B, and
b) this morning with the valve head replaced and everything back to normal, system set to HW and the shower run to use hot water (this caused the boiler to stay lit for 20 minutes trying to heat the HW tank and it tripped the power)

In real life this situation cannot occur. With the Boiler switch set to HW only, there is no power applied to the mid-position valve. The boiler gets its power direct from the thermostat on the side of the tank

If you look at the wiring diagram for an Apollo with a Y plan configuration shown below, you will see what I mean

Now the mid position valve is a strange beast, with some fancy components to make it work, particularly when keeping it in the mid position. Reading what you have said I am thinking that possibly the actuator of the valve has gone.

Provided the Honeywell valve is not too old you can replace the actuator without de-plumbing the valve

It seems that the boiler works fine with the front panel hanging down (as it has been for the last week!) but as soon as I replace it the power tripping problem re-occurs. Trouble is, I can see no obvoius reason why this would be the case - there are no bare wires that would be brought into contact with the casing/front panel and I cant understand why it would happen after 15-20 minutes and not as soon as the boiler comes on.

I think this is just coincidence.

 

[Tyers999]

I know this is ages since you posted and will be amazed if I get a reply but did you find the solution to your boiler cutting the power?? Only I have the same system and it's doing the same thing!! I know nothing about boilers but can pass this info on to someone who does.

Heres Hoping...............

 

[wapit]

ok so I also have exactly this problem, did you fix it?