Panic! the heat pump is going to freeze up

In heat pump land we are hounded by our manufacturers and suppliers , they tell us that the units might freeze up. People really panic about this stuff. Why?

A heat pump is just a big box in the garden, its connected to the house using water pipes, which, if your installer is good, will be insulated. The theory is that because water freezes at 0 degrees C there is a possibility that the water in the pipes or the unit in the garden will freeze in cold weather. Water expands when it freezes with incredible force, so it can split pipes or components in the heat pump. I guess we would like to avoid this.

To stop the water freezing there are 3 things you can do:

1 Put antifreeze in the water, just like you do in your car, put in some Glycol which drops the water freezing temperature maybe to -15C.

There are 37.3 million cars in the UK, they have water and glycol in the radiators. When did you last have a car spring a water leak?

Glycol works well, but it is thicker than water so its harder to pump around the system, it costs a few quid, it slightly lowers the amount of heat the water can absorb so you have to run it a tiny bit quicker through the system and if it leaks on your carpets it leaves a horrible blue stain. (other colours are available). Oh! and its a pain int he backside to pump it into the system.

2 Put anti freeze valves on the system.

Anti freeze valves are designed to open and let the water out the system if the pipes get close to freezing. Its a good idea in theory, it works, but I'm not a fan. Sorry. Emptying the system of water means that you have to refill the system if these valves open.

When you refill the system its really hard to get the air out, you have to put more inhibitor in too, you cant just open the filling valve and hope.

So its cold, the water drains out, the unit stops and now wont work until the plumber comes to site and she's busy cos guess what?, its cold. So you could easily be without heating and hot water because the stupid valves opened.

3 get the unit to look after itself.

Every heat pump has a freeze up protection programme, it works like this,

Most of the time the unit is running in heating when its cold outside, so the pipes are warm and there is no risk of freeze up.

If however the unit is off, (maybe you are on holiday) and the water inside the unit drops below 10 degrees C the water pump and the heat pump is started, the unit never lets the pipes get below 10C, this is stage 1,

stage 2 , If the ambient temperature is below -2C the water pump runs constantly. This keeps the water moving, moving water is harder to freeze.

So the unit doesn't freeze as long as the power is on.

But what happens in a power cut? If the weather is really cold, below freezing and the power is off, the unit cant help itself, this is what the antifreeze and the valves are there to help with.

But think about this:

An outdoor mounted oil boiler (see photo) is just a big box in the garden, its connected to the house using water pipes, which if your installer is good will be insulated. The theory is that because water freezes at 0 degrees C there is a possibility that the water will freeze in the pipes, or the unit . Water expands when it freezes with incredible force, so it can split pipes or components in the heat pump. So the idea is we would like to avoid this.

No one uses glycol or anti freeze valves on oil boilers

If there is a power cut the oil boiler stops. It cant protect itself.

sound familiar?

Have you ever met anyone who's had an oil boiler freeze up? They are as common as people who have had their arm broken by a swan.

If you do meet a unicorn who's had an oil boiler freeze up, ask them what they did to get it fixed ? I bet they called the house insurance company and claimed for a new boiler, just like you would if your pipes froze in the loft.

I think we are protecting ourselves from something that never happens. my rationale behind this is I've worked in heat pumps for 15 years, I sold 10,000 of them. Guess how many froze up? 2

In the first case the home owner switched off the power in January and went on holiday for 2 weeks (dick) and the second the customer was pissing around with the unit experimenting by forcing it into defrost to see what happened. Both didn't have anti freeze or anti freeze valves.