Draining CH system with combi left on for DHW?

[BwanaBanana]

I've drained my central heating system a number of times in the past to replace rads / re-route pipes. Each time I've switched off the combi boiler (Vaillant ecoTEC pro 28 combi) completely.

I was wondering if it's possible to leave the boiler *on* in 'direct hot water only' mode when the system is drained, so I won't be without hot water from the taps while I'm working on the system.

I'm guessing the answer's NO, but I'd like an informed opinion.

Many thanks.

 

[mogget]

The boiler needs to circulate water through the main and secondary heat exchangers in order to provide hot water.

This water is the same water as that in the heating circuit, so with the system drained you would be running the boiler dry - destruction would ensue.

 

[BwanaBanana]

Thanks for the explanation mogget. Just what I was after. As before, I'll switch off the whole lot.

 

[mth]

This water is the same water as that in the heating circuit, so with the system drained you would be running the boiler dry - destruction would ensue.

Feel free to correct me if I'm wrong, but can you not close off the C/H flow and return valves inside the boiler and then drain the the C/H system leaving the boiler and heat exchangers full of water (and still able to use DHW)?

 

[mogget]

I'm no expert, but can see what you're saying. I would be concerned about two things.

1) That the valves may leak if disturbed, and

2) That the boiler may not be able to dissipate excess heat when the demand for HW ends.


Hopefully someone who knows will be able to give us a definitive answer.

 

[bengasman]

This water is the same water as that in the heating circuit, so with the system drained you would be running the boiler dry - destruction would ensue.

Feel free to correct me if I'm wrong, but can you not close off the C/H flow and return valves inside the boiler and then drain the the C/H system leaving the boiler and heat exchangers full of water (and still able to use DHW)?

no

 

[gas4you]

I don't really know about the Ecotec Pro, but certainly the Ecotec Plus, with it's built in filling loop can be run as a water heater only.

One of the plus points given on the Vaillant training course.

 

[mth]

no

Perhaps not on the OP's model, but you can on mine

 

[gavinda]

obvviuos thing to do would be to check your manual if you have it. it would usually state in there if its an approved operation.

 

[BwanaBanana]

OK. I'm not doing the work until this weekend, so I'll definitely check the manual to see if it's possible with my model.

If I'm in doubt, I'll just switch the lot off.

Many thanks for everyone's input.

BB