Boiler Overheat

[robbiecookie101]

Hi guys

I hope you can offer me some advice...

My boiler keeps going into overheat if I set the boiler thermostat too high - if I keep the thermostat at around 50-60% I have no problems but any higher and the boiler goes into overheat - is this normal?

I first adjusted the thermostat as it was taking far too long to warm up the rooms even though the radiators were hot to touch.

I was issued with a gas safety certificate 2 weeks ago so presumably everything should be ok?

My hot water cylinder also have a thermostat on it and is currently set 70degrees.. should I try and lower this?

Many thanks for your help guys

Robbie

 

[stem]

OK, the boiler overheat is there to switch off the burner in the event of the boiler thermostat failing to switch off in order to stop the water actually boiling.

So why is yours tripping? Possibility one, is that the boiler thermostat has gone off calibration, so that when on the high setting it is heating the water in the boiler higher than the overheat and so tripping it, or the overheat has become too sensitive and is tripping before it should. This can only be checked by measuring the flow temperature from the boiler and comparing it to the manufacturers specifications.

Possibility two, is related to the heating system radiators and pipework rather than the boiler itself. When the heating is switched off by the room thermostat or programmer, the burner goes off but there can be residual heat in the boiler internals. If there is not sufficient water circulation in the system, if a motorised valve has closed for example, stopping flow, this can cause the temperature of the water in the boiler to exceed the overheat set point and trip it.

To prevent this, depending upon the type of system / boiler that you have, there may be either a radiator or towel rail that is not fitted with a thermostatic radiator valve, or manual isolation valve, that can accept the supply of hot water, Sometimes a by-pass loop with a control valve is fitted to allow the water to circulate around that for a few minutes whilst it cools. Of course the pump will also need to run on after the boiler goes off to circulate the water. so,

1. Is there a manual by-pass valve somewhere? and if so, is it open enough to allow sufficient water to pass. (some newer boilers may have an internal by-pass)

2. Is there a radiator that is not fitted with a TRV, or not switched off that acts as a by-pass?

3. Does the pump continue to run for a few minutes when the boiler goes off?

Some additional information as to the type of boiler you have, and if you have a Y Plan, S Plan or gravity hot water / pumped central heating system etc., would also be useful.

 

[muggles]

It could also be that the OH stat is faulty...

Please note that a Gas Safety Certificate is just confirmation that the boiler is safe to use, it does not necessarily confirm that the boiler is fully functioning with no faults.

 

[45yearsagasman]

Cylinder stat should be 60 max. Your boiler remains a mystery.

 

[robbiecookie101]

Hi guys

Thanks for the replies so far

Stem - Answers are below!

1. Is there a manual by-pass valve somewhere? and if so, is it open enough to allow sufficient water to pass. (some newer boilers may have an internal by-pass)

I'm not sure what would one look like and where would it usually be fitted?

2. Is there a radiator that is not fitted with a TRV, or not switched off that acts as a by-pass?

No - my flat has just 4 radiators and they are all fitted with TRV's

3. Does the pump continue to run for a few minutes when the boiler goes off?

Yes - The pump was replaced approximately 1 year ago and I can hear / feel it running

Some additional information as to the type of boiler you have, and if you have a Y Plan, S Plan or gravity hot water / pumped central heating system etc., would also be useful.

my boiler is a 'Baxi Solo 2 30 PF' i'm not sure what you mean by y plan s plan etc.

I have cold water and header tank in my loft


As suggested i've turned down the thermostat on the hot water cylinder to 60 but this doesn't help.

Here's a pic showing the highest setting I can have my boiler on without having any overheat issues

Untitled

• robbiecookie101
• 21 Jan 2015
• 1

After turning up the knob I get the overheat light - approx 5 minutes later

Untitled

• robbiecookie101
• 21 Jan 2015
• 1

Is this normal?

Thanks again
Robbie

 

[stem]

Sounds like there may be insufficient circulation in the system. If there's no by-pass, there should be at least one radiator without a TRV on. If you can, unscrew one of the TRV heads so that the radiator is on maximum. Then turn the boiler up and see if it trips then.

 

[Agile]

It is not normal, but that is not the point.

The maximum you should be setting the flow temp to is 82 C.

An ideal boiler design will not allow the temp to be turned up above the temperature at which the over heat stat trips.

But your boiler is old and if not very fully maintained the settings and calibration of components will drift and this kind of problem can occur. But properly set will not cause any problems if you don't turn it up to maximum. ( Why do tenants always expect to turn everything up to maximum? )

Your system should either have a bypass or one rad should not have any TRV. I suppose you have all TRVs set at maximum too. But if you don't have a bypass then you should really remove one TRV head and that should be the one in the room with the room thermostat.

You do have a room stat don't you?

Tony

 

[stem]

Click here for a photo of a by-pass. it's the red valve at a jaunty angle. It allows water to flow through the boiler when any associated control valves are closed, or partially closed. This is a fairly typical installation, but they can be installed in other places.

Google will help with S and Y plan definitions. (other search engines are available)