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[dhcm]

I have got a Vaillant ecomax boiler mounted it the garage. All the external pipes are lagged and there is a frost protection thermostat. I am thinking of installing a pipe thermostat as when the outside temp is near zero (+1 or2)degC, the boiler is running all the time. Would this be a good idea and how should it be wired in? In series with the frost thermostat?

[SimonD]

The ecoMAX has an inbuilt frost protection sensor, so adding additional ones outside will not stop it coming on.

As the frost protection is a component on the PCB there is no way of wiring it in.

[dhcm]

The frost protection is from a wall mounted stat located some two metres from the boiler. This connects back to the control card for the boiler. I have connected a pipe sat on the return feed to the boiler. The pipe stat is connected in series to the frost stat so that when the return is at about 20 deg C the boiler turns off.
This seems to work fine and i'm sure i have saved a hell of a lot of gas over the last two months.

[SimonD]

I think you may be missing the point.

The Vaillant should not be switched with an external frost stat, otherwise it will cycle on and off all the time, because the garage area is unheated. You have just stopped it cycling when the pipe reaches 20 degs. As soon as the pipe drops to 19 degs what happens???

If you took out both frost stats, it would warm itself periodically and then turn off for ages. Adding a second one as a high limit stat is not the answer.

It is light years away from the two stage protection system in the boiler, which spins the pump stage 1 to bring heat from the warmer parts of the house into the boiler, only on stage 2 if that doesn't work, does it bring on the boiler at low modulation.

If you think your old fashioned method saves more gas than the system outlined above, I suggest you may be deluding yourself. It's already in the boiler, you should leave it alone if you want to save energy.

[dhcm]

Thanks for your point. The external frost stat was put in by whoever installed the system -not me- and I guess what your saying is that i can take out the ext frost stat, my pipe stat and everything will be ok? The installation manual says " To protect remote or exposed parts of the heating system or property additional frost protection measures MUST be taken such as the installation of an external frost thermostat connected between terminal 3 & 9 of the junction box to operate both the boiler and the heating circuit". Are you saying this is not necessary?

[SimonD]

No, I'm not.

Your manual will also describe the two stage internal frost protection, agreed?

If you want to protect other parts of the system from frost apart from the boiler, then you would site a remote frost stat in that area, wired to open the heating valve covering that vulnerable zone so the boiler heats that area.

Your post suggests that just the boiler is in the frost danger area and that you were concerned about the cost of the boiler firing up a zone - a zone, no doubt inside the house rather than in the frost risk area?

Therefore, if this is the case - and I haven't seen your house - the internal measures inside the boiler alone will provide the protection you need at minimal energy cost, and moreover the ones added will only waste energy and bypass the excellent measures Vaillant charged you for when you bought their product.

[dhcm]

There's no need to get so worked up about this.
The heating system, boiler, external frost stat etc were all part of the new house when we moved in and was presumably installed by a qualified person. The manual does does not go into technical detail about how the frost protection works. All I was aware of was that on very cold nights the boiler was running all the time & my installation of a pipe stat fixed that. But if, as you say there is no need for an external frost stat then ok maybe i will give it a try, if we get any more cold nights.
Thanks for your input.