central heating some questions

[jack8]

Hello

Hope someone can help with this:

1. I have been looking to buy a room thermostat kit (the room thermostat and I imagine there is a gubbings that needs to be fitted to the boiler itself) for a Worcester Bosch 35CDi. It is a discontinued boiler so finding it difficult to find the kit to buy. Can anyone suggest?

2. I've read stuff on the net and wondering if I udnerstand this correctly so will ask the experts. For a combi boiler system without a room thermostat, am I right in thinking that if you set the CH for on the boiler at 2/3rds of the max, say for illustration sake that is 60 deg, the boiler will heat up the water to this temp and pump it round the system. Until the water temp on the return (after its been through rads) is also 60 deg it will continue to heat the water. Once the 60 deg return is reached then the the burner will turn off until the water in the rad system cools and then reignites the burner to heat the water back to the 60deg through the sytem.

3. Assuming the house is cozy enough on either 2/3 or Max on the sytem as above is it best to keep the CH temp setting in winter to 2/3 or Max to get the best heating for the house and the most cost efficient? I'm regulating temp in each room with the rad valves.

I've been doing some testing over time with various settings but frankly they seem inconclusive since outside temp changes so dramatically round here.

Thanks for any help.

 

[Agile]

Any two wire stat or programmable stat can be connected to your boiler.

There are a wide range of different features and prices!

Tony

 

[D_Hailsham]

Tony has answered your first question but not the other two, so I'll have a go.

2. I've read stuff on the net and wondering if I understand this correctly so will ask the experts. For a combi boiler system without a room thermostat, am I right in thinking that if you set the CH for on the boiler at 2/3rds of the max, say for illustration sake that is 60 deg, the boiler will heat up the water to this temp and pump it round the system. Until the water temp on the return (after its been through rads) is also 60 deg it will continue to heat the water. Once the 60 deg return is reached then the the burner will turn off until the water in the rad system cools and then reignites the burner to heat the water back to the 60deg through the system.

The boiler thermostat setting determines the temperature of the water leaving the boiler. Heat is extracted from the water as it passes through the rads, so the temperature of the water goes down.

If the water returning to the boiler was at the same temperature as the water leaving the boiler no heat would have been extracted!

When the boiler initially starts the flow temperature will be the same as the return, but as the system continues to heat up the flow temperature will rise faster than the return temperature.

Assuming the house is cozy enough on either 2/3 or Max on the system as above is it best to keep the CH temp setting in winter to 2/3 or Max to get the best heating for the house and the most cost efficient? I'm regulating temp in each room with the rad valves.

If the house is warm enough with the stat at 2/3, there's does not seem to be much point setting it any higher. However, setting it to a higher temperature will mean that the rads give out more heat, so the house will heat of from cold faster.

When the house is cold the room stat will be calling for heat, so the boiler stat will control the water temperature. When the house is up to temperature the room stat will turn the boiler off and the water will start to cool down. How long the boiler is off will depend on how well the house is insulated and the room stat differential (about 1C on modern stats). How far the water cools will therefore depend on how long the boiler is off. When the boiler relights it may not even get up to the boiler stat temperature before the room stat shuts the boiler down again.

This means you might as well leave the boiler stat at max (no more than 75C) and let the room stat control everything.

I assume you mean that the rads have thermostatic valves (TRV). If so the room where the wall stat is located shouldn't have a TRV. THis is because the thermostat (wall or TRV) set to the lower temperature will control the room temperature. If this is the TRV, the wall stat will never reach temperature, so the boiler will not get turned off.

If you have a TRV on every rad, set the one where the wall stat is located to Max.

 

[jack8]

Thanks Tony, I didn't realise that you could fit any available so that's good to know. Boiler is due for a service in Jan. Should I buy a kit myself for the service chap to install at time of service or should I contact him and discuss first?

D Hailsham - thanks for those explanations. The system currently doesn't have a room thermostat but I think I can work out what you meant anyway. Yes I did mean TRVs. Thanks.

 

[D_Hailsham]

Should I buy a kit myself for the service chap to install at time of service or should I contact him and discuss first?

Installing a thermostat is not part of a service, so you need to discuss it with him first.

If you want something which is reliable, go for Honeywell. The are slightly more expensive, but worth the extra. Make sure you get a digital stat.

The system currently doesn't have a room thermostat

The quicker you get one, the better. It will pay for itself very quickly.

 

[jack8]

D Hailsham, thanks again for that info.

I'm obviously not the best at communicating sometimes Of course I would discuss with the boiler chap if he could install thermostat at the same time of service.

What I meant to ask was, since Tony said 'a two wire' thermostat I was wondering if I should as the boiler chap which kits are suitable for my boiler. Or can I buy any wireless thermostat (as long as it has the functions I need)? Also the boiler has a timer and stuff built into it, when a programmable wireless room thermostat is installed, is the timer gubbins on the boiler overriden or disabled?

I was looking at the Honeywell models as they seem to have good flexibility and good reviews.

Thanks and sorry for lots of questions.

 

[D_Hailsham]

Can I buy any wireless thermostat (as long as it has the functions I need)?

Yes.

the boiler has a timer and stuff built into it, when a programmable wireless room thermostat is installed, is the timer gubbins on the boiler overriden or disabled?

You can do either. Disabling is probably hte better option as it then prevents anyone fiddling with the timer. If you want to override it, you just set it to the permanently on or continuous position for central heating.

The Honeywell CM927 has a very good reputation and can be used with your boiler.

 

[jack8]

Thanks again for this info, I had been looking at that Honeywell model as an option, and also thanks for taking the time to help. Appreciate it.

Cheers