Boiler constantly turning on and off

[Fordy81]

no. It sounds like it is jammed. You should be able to turn the spindle with your fingers. Does it need pliers?

Sorry John, what spindle exactly?

 

[JohnD]

the three port valve has two major parts.

A brass valve, with spindle which moves a rubber ball inside to block or open the outlet ports; and the electrical motor and switch, which rotates the spindle in response to voltage down the control wires.

Unless your valve is very old, you will be able to see how to remove the motor assembly from the valve assembly.

 

[Scarum]

If the spindle under the Myson 3 port valve is stiff it sounds like rust has caked up in the valve and causing the actuator motor to heat up and it could burn out.

After a half drain of the system with 3 port valve in mid position (I did mine from the boiler) the spindle can be removed (two retaining screws under the actuator). I took the spindle from a new identical Myson valve body (careful when you remove, there are small springs with two 'shoes' inside!) Clean as well as you can in the valve body and fit new spindle. You could replace the whole valve if you got the spanners and the nuts aren't tight as hell (as mine were.)

You should clean the FE tank so it's spotless. Careful you don't work any of the muck in to the feed pipe... mop the crap up in to a bucket. If you do above dont forget more inhibitor!

 

[Fordy81]

Ok, so I drained the system, cleaned the F&E tank which was complete sludge at the bottom, added X800 first, draining it 4 times after until the water was clear. Refilled the system and added X400. Just after adding the X800 all the rads got hot really quickly. Didn't have to balance the rads at all.

Boiler now runs for a lot longer first time than before. 15 minutes or so which is about double the time. But then it carries on with the constant on and off.

Bought a magnet and there is some sediment stuck to the pipes above the pump and in the aerator (think that's what it's called, looks like a small tin can). But I don't think there is a lot going by the magnets hold on it. Presumably I really should remove this? Especially as it's above the pump and if it comes loose it's only going one way?

Also, should I be thinking about adding a magnaclean to the system. There isn't enough room on the return pipe to the boiler but I think it's ok to add it above the pump in the airing cupboard?

Any other ideas why the boiler might keep cutting out though?

Cheers folks

 

[kbdiy]

Assuming all you controls/valves are functioning correctly then the switching on and off of the boiler sounds perfectly ok to me. I have a Suprima as well so am familiar with normal operation. Boiler fires and heats the water - boiler stat cuts off at the set point. As the heated water circulates it gives up heat through the rads and returns cooler to the boiler. Boiler fires again to heat the cooled water, boiler stat cuts off again and so the cycle is repeated. Depending on the demand for heat (or hot water) the boiler will continue to cycle in this way until the cylinder/ room stats cease demand.

The boiler is designed as low water content so I would expect fairly short cycles of heating as there is only a small heat exchanger capacity.

Remember too that the Suprima needs a bypass circuit as it has an overrun facility to remove excess heat from the boiler AFTER all demand has ceased.

Don't confuse the operation of this boiler with that of a more modern modulating boiler as the two are considerably different.

 

[stem]

You actually worked it out yourself in your first post.

..it seems as though the boiler is reaching the max temp in similar times at the start so shuts down? Then takes similar times to cool down enough to fire back up?

The boiler thermostat switches the burner on and off to keep the hot water leaving the boiler at the set temperature (plus or minus a degree or two)

As the radiators, pipework, rooms etc., warm up, the 'on' time gets less and the 'off' time increases. Exactly what your figures show.

I timed the boiler and below is the times of on and off;

On - 2m52s
Off - 2m12s
On - 1m22s
Off - 2m12s
On - 1m02s
Off - 2m12s
On - 50s
Off - 2m30
On - 40s
Off - 2m39s
On - 39s

Sounds like you may have a problem with the external controls though if the house is getting to 25 degrees when the room thermostat is only set at 20 degrees. Unless you have massively oversized radiators that release a lot of heat after the system goes off, or another heat source somewhere.

 

[Fordy81]

Assuming all you controls/valves are functioning correctly then the switching on and off of the boiler sounds perfectly ok to me. I have a Suprima as well so am familiar with normal operation. Boiler fires and heats the water - boiler stat cuts off at the set point. As the heated water circulates it gives up heat through the rads and returns cooler to the boiler. Boiler fires again to heat the cooled water, boiler stat cuts off again and so the cycle is repeated. Depending on the demand for heat (or hot water) the boiler will continue to cycle in this way until the cylinder/ room stats cease demand.

The boiler is designed as low water content so I would expect fairly short cycles of heating as there is only a small heat exchanger capacity.

Remember too that the Suprima needs a bypass circuit as it has an overrun facility to remove excess heat from the boiler AFTER all demand has ceased.

Don't confuse the operation of this boiler with that of a more modern modulating boiler as the two are considerably different.

Oh ok. It's just the fact it was shutting off before the rads got hot. Hopefully the cleaning of the system has cured that now, which I think it must have seeing as though it stays on for longer to start with.

Can you elaborate what a bypass circuit is? In my airing cupboard, I have an isolation valve that is off (always has been) that presumably takes water away from both the hot water and CH? Is that what it is?

Untitled

• Fordy81
• 25 Jun 2014
• 2

Untitled

• Fordy81
• 25 Jun 2014
• 4

 

[Fordy81]

You actually worked it out yourself in your first post.

..it seems as though the boiler is reaching the max temp in similar times at the start so shuts down? Then takes similar times to cool down enough to fire back up?

The boiler thermostat switches the burner on and off to keep the hot water leaving the boiler at the set temperature (plus or minus a degree or two)

As the radiators, pipework, rooms etc., warm up, the 'on' time gets less and the 'off' time increases. Exactly what your figures show.

I timed the boiler and below is the times of on and off;

On - 2m52s
Off - 2m12s
On - 1m22s
Off - 2m12s
On - 1m02s
Off - 2m12s
On - 50s
Off - 2m30
On - 40s
Off - 2m39s
On - 39s

Sounds like you may have a problem with the external controls though if the house is getting to 25 degrees when the room thermostat is only set at 20 degrees. Unless you have massively oversized radiators that release a lot of heat after the system goes off, or another heat source somewhere.

Oh ok. This is actually my first real experience of boilers. Always had gas fires before that. lol

Well that's a relief. lol

Oh and fixed the problem with the temp continuing to rise with a new room thermostat.

 

[kbdiy]

The bypass circuit will be a pipe from the flow to the return after the pump but before the 3-port valve. It will have some sort of valve in the pipe, might be a manual gate valve or similar, but it should not be fully closed otherwise the overrun will not work correctly. Conversely if it is set too far open it will short-circuit the flow to the cylinder and rads and they will not get fully hot.

 

[Fordy81]

The bypass circuit will be a pipe from the flow to the return after the pump but before the 3-port valve. It will have some sort of valve in the pipe, might be a manual gate valve or similar, but it should not be fully closed otherwise the overrun will not work correctly. Conversely if it is set too far open it will short-circuit the flow to the cylinder and rads and they will not get fully hot.

So it is that isolation valve in the pic above then?

I've given it a quarter turn so it's half open.

Thanks.

 

[kbdiy]

Possibly but I can't see enough of your pipework to give advice on that. You should be able to check by tracing the flow and return from the boiler and seeing where they are linked via any sort of valve.