Frost protection on combi boiler

[Rocboni]

Quick hypothetical question,

Combi boiler in garage with frost stat and pipe stat on return pipe, two zone valves for upstairs and downstairs, does the frost stat have to open one of the valves or just fire the boiler? Do they have a bypass valve?

 

[Leesparkykent]

You want it to turn the heating on so the pipes get warm.

 

[Rocboni]

I understand that but can it circulate water without opening the valves, as your only wanting the pipes to get hot?

 

[Leesparkykent]

Depends where the bypass is. Some are internal to the boiler some will be in the cylinder cupboard which you haven't got as it's a combi.

 

[Octopus]

I would be consulting the manual for the boiler in question....

 

[ruston]

So would I , it will depend whether you just want the boiler protected , ie located in a garage , or if the system is at risk from frost too - all depending on the/your location.

 

[onions1066]

How old is the boiler??

 

[Rocboni]

How old is the boiler??

There isn't one, I was just wondering as I've seen it done on new boilers, but they did not open the valves as far as I know so they must have an internal bypass?

 

[Leyland30]

A frost stat on the boiler is intended to protect the boiler from frost damage. A A stat internal to the property will independently fire up the boiler if it detects a risk of frost within the house for instance I.e. Opening up valves.

In answer to you question - just fire up the boiler.

 

[davesparks]

A frost stat on the boiler is intended to protect the boiler from frost damage. A A stat internal to the property will independently fire up the boiler if it detects a risk of frost within the house for instance I.e. Opening up valves.

In answer to you question - just fire up the boiler.

However the heat from the boiler needs to go somewhere,

 

[Leyland30]

Dave, the boiler will heat up until the frost stat upper limit is satisfied. If the heat can't go anywhere all the better.

 

[davesparks]

Dave, the boiler will heat up until the frost stat upper limit is satisfied. If the heat can't go anywhere all the better.

if the heat can't go anywhere the boiler will overheat and lock out, a modern boiler is too well insulated to leak enough heat to warm up the surrounding air and operate the frost stat. A pipe stat is required in series with the frost stat and fitted to the return pipe to the boiler.
Also when the boiler fires the pump will run, if the heat can't go anywhere then it will be pumping against the closed valves, hardly an ideal situation.

 

[Midwest]

Seem to recall some manufacturers have an internal frost protection, Worcester Bosch Greenstar for example;

'The boiler has inbuilt frost protection. When the primary temperature drops below 8°C the pump is switched on. When then temperature rises above 9°C the pump switches off after a 3 minute pump overrun. If the primary temperature drops below 5°C, a central heating demand is activated until the primary temperature rises above 12 °C. The demand switches off followed by the pump after a 3 minute overrun.

The boiler has the facility to connect an external frost protection device to protect in “at risk areas” (terminal block ST6, contacts FS and FR). This is used if the boiler is not located in the area needing protection i.e. boiler in kitchen but pipe work in the garage that needs frost protection.
If external frost thermostat is calling, i.e. temperature within frost thermostat below the set point, but the primary temperature of the boiler is above 5°C, the pump will run until the temperature within the frost thermostat rises above the set point. If external frost thermostat is calling and the primary temperature is below 5°C, a central heating demand is activated until primary temperature is above 12 °C. If the frost thermostat is still calling the pump will run until the temperature within the frost thermostat location rises above the set point'.

The internal pump operates an internal bypass valve, when frost protection is required (8-5'), or CH demand (using external valves etc) when below 5', or so I believe.

So hypothetically, if the boiler was in a garage, with short lagged pump runs, just the internal frost protection could be relied on.

Edit: If you are looking to do such an install, can I suggest you consult a competent plumber, gas safe registered to install your new boiler

 

[davesparks]

Seem to recall some manufacturers have an internal frost protection, Worcester Bosch Greenstar for example;

'The boiler has inbuilt frost protection. When the primary temperature drops below 8°C the pump is switched on. When then temperature rises above 9°C the pump switches off after a 3 minute pump overrun. If the primary temperature drops below 5°C, a central heating demand is activated until the primary temperature rises above 12 °C. The demand switches off followed by the pump after a 3 minute overrun.

The boiler has the facility to connect an external frost protection device to protect in “at risk areas” (terminal block ST6, contacts FS and FR). This is used if the boiler is not located in the area needing protection i.e. boiler in kitchen but pipe work in the garage that needs frost protection.
If external frost thermostat is calling, i.e. temperature within frost thermostat below the set point, but the primary temperature of the boiler is above 5°C, the pump will run until the temperature within the frost thermostat rises above the set point. If external frost thermostat is calling and the primary temperature is below 5°C, a central heating demand is activated until primary temperature is above 12 °C. If the frost thermostat is still calling the pump will run until the temperature within the frost thermostat location rises above the set point'.

The internal pump operates an internal bypass valve, when frost protection is required (8-5'), or CH demand (using external valves etc) when below 5', or so I believe.

So hypothetically, if the boiler was in a garage, with short lagged pump runs, just the internal frost protection could be relied on.

Edit: If you are looking to do such an install, can I suggest you consult a competent plumber, gas safe registered to install your new boiler

Indeed they do, but it's not every model of Worcester boiler which has this so you have to read the instructions every time.

 

[Midwest]

Indeed they do, but it's not every model of Worcester boiler which has this so you have to read the instructions every time.

I can help the OP there, according to WB technical, only the CDI Regular hasn't internal frost protection.

But perhaps get a competent gas certified installer to read the instructions instead.