Myson Apollo 50Si Hi Stat

[Pilotjet]

Folks, would be grateful for any information on my Apollo 50Si. This boiler was installed when the house was built 20 years ago so already has had a good innings, but I'd like to keep it soldiering on for while yet.

The system is a conventional open vented F & E installation in microbore with motorised valves on the DHW and CH. Hot water cylinder is set to 60 degrees. The pump is a Grundfoss UPS 15-60 running at speed setting '3'. There is Sentinal X100 inhibitor in the system.

I normally run the boiler at the Lo setting, but since we've had outside temps down to -16 degrees in Scotland recently, I've needed to use the Hi setting. The outlet temperature (measured via an infra red thermometer) is over 90 degrees C when set to Hi and about 72 degrees C when set to Lo. I put some black insulating tape over a point in the outlet pipe to try and get an accurate reading from the infra red thermometer.

According to the boiler specifications, the maximum flow temperature is only meant to be 82 degrees C. The boiler sounds like it's just on the point of 'kettling' before the Hi stat cuts in and 90 degrees seems a very high temperature to me - I'd have thought about 80 - 85 degrees would be nearer the mark. The rads get very hot when using the Hi stat, but in the recent cold snap, not really hot enough when set to Lo. Ideally I'd like a 'Medium' stat I think!

I have one rad in an upstairs bedroom which tends to need bleeding every other day if using the Hi stat (it's fine if using Lo) so I'm assuming there must be some sort of problem. I've checked the trigger point of the Hi stat (and also a spare replacement) by measuring it in a pan of water - and it does seem to be set for 90 degrees.

Is anyone aware of alternative Hi stats which can be used on the Apollo 50? I'd like to find one which was set to cut in at about 80 - 85 degrees if possible, but I can't see any way of decoding the part numbers to identify the trigger temperature.

Any comments would be appreciated.

 

[washer]

No there isnt. Mind you, it's that old your lucky it's still that accurate!

 

[Billy Bob Bob]

put the inferred thing in the bin you have a corroded system or pump problem or system defect

 

[Pilotjet]

Gas Man - thanks for your comments. I believe the infrared thermometer reading is reasonably accurate as I've crossed checked it against a thermal probe on a multimeter. The pump was replaced earlier this year and appears to be operating correctly.

I think it is inevitable that there will be some corrosion in such an old system (although it has had inhibitor since new), but my concern was the apparently very high temperature of the outlet flow when switched to Hi. I assume an outlet temperature reading of circa 90 degrees is not normal?

I use the Hi setting very rarely as the house usually gets warm enough at Lo, I only noticed this problem during the recent very cold snap. Using a Hi stat which triggered at a slightly lower temperature seemed a reasonable fix, but it appears that this is not an option. Pity the Apollo only has the two settings as simply turning the wick down a bit is all I'm after

 

[Billy Bob Bob]

is it venting over? should do if its getting to hot

 

[tamz]

Most likely nothing wrong with the stat. As said it is a system corrosion problem and a build up of magnetite leading to false readings.

 

[Reg Man]

Hand in pocket. System power flush may get you out of problem (Not guarantead) . But probably new system would be more economic.

 

[shorticus]

check your copper pipes with a magnet, if it sticks then it's a clear indication of magnetite build up i.e. corrosion, as advised above a powerflush may help but it's no gaurantee, it's a days work for someone so will cost a bit

 

[Pilotjet]

Folks, I appreciate you taking the time to respond to this thread - Thanks.

Gas Man - there little evidence of venting over in the F/E tank, if it is doing this, it must be on a relatively minor scale.

Tamz / Reg Man - I've not had any of the 'classic' symptoms of sludge build up as the rads do get hot at the tops and bottom. The largest rad in the house is slightly cooler at the bottom-middle, but on a 20 year old system I suppose that is to be expected. I tend to think that if it's got bad enough to need a powerflush, it's probably game over.

Shorticus - As you suggested I checked the copper pipes with a magnet and none of the microbore pipes to the rads were affected. I have a Spirotech Magnabooster 2 on the return line before the boiler so I assume that must be helping a bit. However, when I checked the 22mm outlet pipe from the boiler, that did shows some sign of magnetic attraction. I guess that means that the heat exchanger will be suffering the same problem and new boiler time is not too far away

The outlet pipe from the boiler exits at the top and is roughly an upside down 'U' shape about 1 meter in length with the F/E feed in the middle of the 'U' if that makes sense. The pump is fitted at the end of this 1 meter length of pipe and pumps down towards the valves. Interestingly, there is no magnetic attraction in the piping past the pump, it seems to be confined to this short length only. As it is easy to access this section, I'll try replacing that section of pipe and will flush the boiler heat exchanger with mains water to see if that helps.

To be honest, the main reason I'm reluctant to junk the present boiler is that I've so little faith in the newer condensing models - even 'good' makes seem to have all sorts of problems and their durability seems rather questionable. Based on my experience with it, if I could replace the Apollo with another one exactly the same, I'd do it without hestiation as it's been really reliable.

BTW: I had a go at deciphering the printed information on the Hi stat. The Apollo uses a Thermodisc 36TXE21 switch. Thermodisc don't sell direct to the public, but if you have a look here: [DLMURL="http://www.tradepar.co.uk/search/temperature-switch.html"]Temperature Switch - Search - Tradepar Shopping[/DLMURL] other thermostat values can be obtained.

Again, thanks to those who have taken the trouble to reply. You'll probably see a new thread shortly with the inevitable 'What's the best boiler' questions!