Myson Apollo Boiler Cutting in and out every 20 secs.

[Kspencersmith]

Central heating system was blocked . Has now been flushed out, pump replaced and motorised valve replaced.
All radiators now heating up and hot water, but boiler cutting out and firing up again every 20 seconds.

 

[Agile]

It sounds as if the flow rate through your boiler is still too low.

It needs to have the temperature differential across the boiler checked. It should be about 11° C.

Pump should be on "2" but you could see what effect putting it on "3" has. I expect that may keep the boiler firing for longer.

The power input to the boiler may also be too high but that needs a CORGI to check. Thats less likely though.

Tony

 

[undercover]

Or you could just have an airlock......

 

[D_Hailsham]

It needs to have the temperature differential across the boiler checked. It should be about 11° C.

Apollo's are strange beasts. Depending on the version, they say the drop across the radiators should be set to 10°C or 11°C with the by-pass open one turn and then the by-pass is adjusted to give 8°C or 9°C drop at the boiler.

 

[Agile]

The correct ( automatic ) bypass does not open by "turns" but according to a scale showing the head pressure which causes a flow through.

That suggestion must be based on the old bodge of using a gate valve !

Tony

 

[nickso]

i dont know when auto bypasses were invented and became freely available on the UK market, does anyone know?

the oldest ones i have seen seem to be around the ten year mark, does this mean anything beyond that was a bodge because the equipment to do it properly was not available?

 

[Kspencersmith]

I was thinking air lock as I did have blockage on downstairs radiators which seemed to improve when system was left to settle for a few days and then air released through air vent by cylinder.

If it is an airlock in the boiler how can it be released.

Appreciate all comments about temperature differences and balancing valve, hope to try air lock first with some advice.
Thanks

 

[D_Hailsham]

The correct ( automatic ) bypass does not open by "turns" but according to a scale showing the head pressure which causes a flow through.

I agree that an ABV is the correct way, but the setting will depend on what drop you are trying to obtain across the boiler. I know it's the flow rate which is important, but how many installers have flow meters? Setting the ABV on the basis of an 11°C drop across the radiator will give a lower flow rate than an 8°C or 9°C drop, which could result in the boiler overheating.

That suggestion must be based on the old bodge of using a gate valve

Bodge is the right word, but why is the boiler drop lower than the rad drop?

 

[Agile]

Bodge is the right word, but why is the boiler drop lower than the rad drop?

I know why but I dont know if I can explain it well enough!

Boiler circulates some of the water through the ABV and some through the rads.

Flow at 82° and return from rads at 71°.

Part of flow through boiler is returned through the ABV to the boiler return and as this is at 82° it has the effect of increasing the return temperature above the returning 71° from the rads giving say 73° back into the boiler.

I wonder why the OP does not want to follow my advice to find the fault?

Tony

 

[Slugbabydotcom]

Apollos were not designed to be used with an ABV! Them days ABV's weren't available but gate valves were. Proper By-pass valves were available if you looked hard enough; but who could be bothered carting them around when they could use a gate valve? More conscientious plumbers of the day would remove the wheelhead. Where the wheelheads were left on it would often be the case that a diyer would come along and close every valve before draining off and after altering their rads or whatever they would duly open every valve creating a short circuit and leaving them wondering why the rads wouldn't get warm.
Unfortunately partsarena.com/baxi only have a maintenance guide listed for most of these boilers but for the 65/80B version[:-
Catalog » Thorn » Boiler » Apollo » 65/80B > S/N 90064564 (GC No. 4178969) » Installation Instructions » Apollo 50/65B & 65/80B]
they state that a by pass kit is available

A pump and by-pass kit is available which positions the pump in a readily accessible position above the boiler, includes a built in by-pass and allows a combined cold feed and vent to be connected directly to the boiler.

No mention of an ABV there, so it ain't a bodge.
I wouldn't fit an ABV to one of these as I believe that as one of the first copper HE boilers they need some pre-warmed water from the start of firing to reduce boiler noise.
Boiler design and technology has improved since then and I dare say pump flow rates have as well so even though an ABV may do the trick as Tony implies I would prefer to stick with the manufacturers instructions in this instance.
I concur with all the other points in this topic

 

[D_Hailsham]

Bodge is the right word, but why is the boiler drop lower than the rad drop?

I know why but I dont know if I can explain it well enough!

Yes, you can! The only bit I would query is:

Boiler circulates some of the water through the ABV and some through the rads.

With the fixed (gate) valve there is always flow through the valve but, with an ABV, the valve is closed until the pressure across the valve reaches the set value, then it opens. So Slugbaby is probably right when he says:

I wouldn't fit an ABV to one of these as I believe that as one of the first copper HE boilers they need some pre-warmed water from the start of firing to reduce boiler noise.

ABVs have become significant with the installation of TRVs on radiators and then only if recommended by the boiler manufacturer. There is no mention of TRVs in any of the Apollo and Apollo Fanfare literature on Partsarena.

 

[Agile]

I was only explaining how the boiler differential could be lower than the heating circuit as a result of a bypass.

I dont see why it should be necessary to have a bypass if there are no TRVs with this model. The design is typical of most non condensing boilers of its style.

The HE is preheated by the pilot light.

So, come on Slug, why does it need a flow of slightly heated water at startup "to reduce noise" ?

No other boiler I can think of has this need and I have never seen an Apollo fitted with a bypass anyway. I have never thought of them as noisy anyway.

The one improvement I would make is to lower the temperature of one or both stats. Few of them can operate reliably on the high setting at this age anyway.

Tony

 

[Slugbabydotcom]

So as the pre warmed water leaves the boiler and is replaced with cooler system water what happens to the temp differential if there is no bypass?

It increases resulting in kettling!

Theres loads of apollos round here and they all have a bypass! I live near to what I am told is europes largest housing estate and many apollos are there still providing good service with a moderate appetite for thermocouples, pilot burners and stats. Plus of course the aforementioned DIY tampering problem to which I still get the odd call

 

[Deleted member 105431]

So as the pre warmed water leaves the boiler and is replaced with cooler system water what happens to the temp differential if there is no bypass?

It increases resulting in kettling!

Theres loads of apollos round here and they all have a bypass! I live near to what I am told is europes largest housing estate and many apollos are there still providing good service with a moderate appetite for thermocouples, pilot burners and stats. Plus of course the aforementioned DIY tampering problem to which I still get the odd call

Blacon in chester?

 

[Agile]

So as the pre warmed water leaves the boiler and is replaced with cooler system water what happens to the temp differential if there is no bypass?

It increases resulting in kettling!

If the water flow rate is correctly set then the differential will stay the same regardless of the flow temperature as it heats up.

Tony