Safety shutoff on Megaflow thermostat

[DavidSWP]

Hi all,

My gas central heating stopped working on Friday. It's an Ideal FF360 boiler which is linked to a Heatrae Sandia Megaflow immersion heater tank.

Plumber called out said the fan in the Ideal boiler had gone. He diagnosed this by checking if any air was being blown out of the exhaust outlet on the outside of the house and quoted £280 to change the fan (£40 callout for that day + £140 for the fan + 2 hours labour to fit it). So anyway the 'backup' electric immersion heater in the Megaflo was also not working, so no hot water at all. I was just reading posts on here looking for common problems and noticed the safety shutoff on the stat had popped out so I pushed it back in. Then went out for a few hours - came home and CH and HW working again.

Could this have been a coincidence or is the stat on the Megaflo cylinder capable of stopping the gas boiler from working for central heating? I don't know if they are linked but it would kind of make sense...

Based on what the plumber said and the fact that the Ideal boiler is 14 years old, has no service history and is non-condensing I plumped for getting a new boiler which he has quoted £1585 all in and I already paid 25% deposit. Now I'm a bit annoyed because I'm thinking there was nothing wrong with it and will probably still have to pay to get the real problem fixed with the Thermostat on the Megaflow. So I'd really appreciate it if anyone can tell me if that can shut of the CH or if it was just coincidence that it came back on after I pushed it back in.

 

[Gasguru]

The overheat thermostat on the cylinder should have no bearing on the CH unless your wiring is incorrect or you have a hot water priority setup (unlikely).

A common reason for the overheat stat tripping is the cylinder zone valve jamming open keeping the boiler on.

It would appear your plumber is clueless....

The Ideal Classic is one of the most reliable boilers ever made...I'd happily have it over any condensing boiler even if it's a little more inefficient.

 

[MeldrewsMate]

Absolutely no connection at all.

The only possible connection could be a thermal one i.e. Immersion heater makes water hot and operates cylinder 'stat, this causes 3 port valve to drive over to CH ONLY position whereupon the 2nd microswitch gives a command to start the boiler. This assumes you have a 3-port heating valve (and should additionally have a two port valve for the Megaflow)

To test, select heating & hot water on the programmer.
Run a bath, or in some other way cause the Megaflow to call for heat.
Does the boiler run (and yes, can you hear/feel air coming out of the flue)?
Select heating only (hot water off), with the roomstat turned up high. Does the boiler still run?

A new boiler will save you money compared to your old lump. The fans on the Ideal Classic FF whatever are prone to failure, and the price he's quoted seems reasonable. Enjoy your new boiler.

 

[MeldrewsMate]

A common reason for the overheat stat tripping is the cylinder zone valve jamming open keeping the boiler on.

I beg to disagree GG.

The effect of the cylinder overheat stat operating (on the immersion heater) would be to stop only it from working.
If the cylinder o'heat operated it would not stop the boiler from heating the house......unless the 2/3 port valve would not drive over to the heating only position....

....could it be that the OP has a stuck two port on the Megaflow supplied valve and a duff sync motor on the other valve?

OK, I'm not disagreeing now, just begging.

 

[DavidSWP]

Hi,

I had to abort the test. I ran a bath with the HW and CH on - no heat from the flue. I think it had already switched itself off again.

I went back to the Megaflow cylinder stat and the safety shut off and popped out again and I could smell an electrical burning from that area. I pressed it back in and checked the boiler pilot light through the spy window and couldn't see anything. Now HW is cold and the radiators are nearly cold again. I then came back to the Megaflow stat and stronger smell of electrical burning from that area. I turned it off at the switch in the cabinet and at the consumer unit.

So would it be fair to conclude that the Ideal boiler just came back on by coincidence and the fan is probably on its way out but can be kicked into life occasionally?

Obviously there is some problem with the Megaflo - probably the element I guess - any ideas? I guess I go ahead with the boiler swap anyway. I take on board that it's a good boiler but £280 is a fair chunk of money and would rather have a new boiler with a 5 year guarentee I think. We never actually use the immersion heater and it was off at the time the CH failed originally. I was only attempting to get it to work to get some HW.

 

[Gasguru]

It's your money but given the plumber hasn't a clue at diagnosing the faults on your system what makes you think the installation of the new boiler will be any good....boiler manufacturers often only honour warranties if the installation is up to scratch.

You realise the faults could all be on the Megaflow/controls so you could be chucking a way a perfectly good boiler and still require further repairs.

What's the proposed new boiler?

 

[DavidSWP]

It's your money but given the plumber hasn't a clue at diagnosing the faults on your system what makes you think the installation of the new boiler will be any good....boiler manufacturers often only honour warranties if the installation is up to scratch.

You realise the faults could all be on the Megaflow/controls so you could be chucking a way a perfectly good boiler and still require further repairs.

What's the proposed new boiler?

Ok, but I thought the general consensus was that it was probably not linked to the megaflo? He did say that the £1585 price was to get it working and that he would not add anything to the cost irrespective of if he had unexpected installation problems. I'll raise these concerns with the plumber anyway. The new boiler will be a Glowworm 18HX

 

[St0rmer66]

In my experience a failed fan is failed for good. If anything they sit there buzzing away, not spinning, getting hotter and hotter and seized even worse.

Sounds like he doesn't have a clue when it comes to fault finding!

 

[DavidSWP]

In my experience a failed fan is failed for good. If anything they sit there buzzing away, not spinning, getting hotter and hotter and seized even worse.

Sounds like he doesn't have a clue when it comes to fault finding!

He just texted me saying that he moved the fan that was seized but it wouldn't move under its own power when he came around on Saturday. Anyway, he says he'll fit it and get the system working for the agreed price and has good feedback from other people + has been around for a while. If he screws up I'll just get his company to sort it out until I'm satisfied. Doubt I can just back out now since I paid a deposit.

 

[MeldrewsMate]

Ok, but I thought the general consensus was that it was probably not linked to the megaflo?

Not at all, we;re going on the evidence you provided.
You said the boiler wouldn't work, but when you put the immersion heater on it cane back to life several hours later.

Now we have new evidence, that the fan is seized...or do we?
And now there's a burning smell near the Megaflow, probably in a different room.

So if the fan is seized then it is U/S and needs to be replaced. If it just isn't turning that could be because the boiler hasn't been commanded to run....do you see the difference?

So to the burning smell; did it go away when you turned the immersion heater off? Or are you not refering to the immersion heater? Did you turn off the immersion heater, or maybe it was the HW function of the heating system, or both? Please re-state what you switched on, off, and approximately when.

 

[DavidSWP]

Ok, but I thought the general consensus was that it was probably not linked to the megaflo?

Not at all, we;re going on the evidence you provided.
You said the boiler wouldn't work, but when you put the immersion heater on it cane back to life several hours later.

Now we have new evidence, that the fan is seized...or do we?
And now there's a burning smell near the Megaflow, probably in a different room.

So if the fan is seized then it is U/S and needs to be replaced. If it just isn't turning that could be because the boiler hasn't been commanded to run....do you see the difference?

So to the burning smell; did it go away when you turned the immersion heater off? Or are you not refering to the immersion heater? Did you turn off the immersion heater, or maybe it was the HW function of the heating system, or both? Please re-state what you switched on, off, and approximately when.

Hi,

We've lived in this house for a little under a year. We always have the immersion heater switched off (via the electical switch in the Megaflo cupboard which is on the floor below the gas boiler) because we don't need it. I've long suspected that it doesn't work since I've tried turning it on before and didn't notice any difference to the amount of hot water. The safety cut-off on the stat has probably been activated since we moved in.

After the CH and HW failed late last week and the plumber came out on saturday, I had a little time today and decided to see if I could get the immersion heater working. I unscrewed the stat cover and pressed in the safety cut-off at about 3pm this afternoon, went out until 9pm and on returning the radiators were warm and there was warm water. I suspect it had actually been on for a bit while we were out but had probably gone off again before we arrived home because everything was just warm, not properly hot.

Then I started writing on this forum and tried to carry out the test MeldrewsMate suggested and decided that nothing was happening with the boiler. I then removed the cover from the megaflo stat at say 9:40 pm. Smelt electric burning from there and the safety cut-out again activated, so I pressed it back in, went immediately to see if the gas boiler was working, it wasn't, so I returned to the Megaflow which now had a stronger burning smell and I turned it off via the electrical switch in it's cupboard and also turned off the switch marked 'water heater' at the consumer unit since I don't want a fire on my hands The electric burning smell from around the megaflo stat is now gone. If it wasn't I would be considering evacuating the house right now...

Thanks for all you advice people.

 

[St0rmer66]

What we're saying is that the boiler might not be even getting the "signal" to fire up in the first place. It might not be faulty, just an external control problem.

 

[DavidSWP]

What we're saying is that the boiler might not be even getting the "signal" to fire up in the first place. It might not be faulty, just an external control problem.

Yes I understand what you're saying and I don't see how turning a fan by hand proves that it was 'seized' rather than just not being 'turned on' either! It sounds like a load of nonsense to me too.

However I think on balance its probably nothing to do with the Megaflo based on what people have said here and because its never worked for the past year and the gas boiler has always been fine. I've made it clear that I expect the boiler to be installed and the gas CH and HW working without issues in the end, and I've told him about my concerns with the megaflo so if it doesn't work because of some issue with the megaflo he's just going to have to sort it otherwise I won't pay him the final 75% and will claim my 25% deposit back. Of course its always better to be informed which is why all your advice is so helpful. I just want the CH and HW sorting really.