Which thermostat has priority on heating system?

DVardysShadow

jennifernil wrote: »

I know it is supposedly "best practise" but I really cannot see the need or sense in having a room stat when TRVs are fitted. Yes, it turns off the pump, but then if one of the TRVs calls for heat it will not get it.

We have TRVs on all rads other than the hall, which acts as a bypass. Our system has been in place over 22 years and works how we like it to work. We have living rooms, study, and bathrooms on 3-4, bedrooms we do not heat at all.

Our house is 280 sq metres and our bill is about £750 for heating and HW.

If we had to have a room stat, we would have it in the hall, set it to MAX and carry on as before.

You've missed the essential knack in designing and setting up a system of this sort. The hall radiator should be slightly undersized, so that the hall does not quite reach 'stat temperature on a cold day. I had this setup in a previous house. It was always the case that if the room 'stat called OFF, it was calling ON before the rooms with TRVs had cooled noticeably.

gas4you

Assuming it is a new condensing boiler, try keeping the boiler stat set to no more than 70c. This should ensure the return temp is below dew point, making the boiler condense more and save you money.

amcluesent

The boiler thermostat (and pump speed, if adjustable) will only change how quickly energy is added to the system, shortening the time to reach the design temp in the rooms. Whacking this up won't make the rooms hotter.

Since you've got the roomstat in the hall, you'll need to set it high enough that the rooms in the house with TRVs get heat often enough to reach desired temps in the room ands the heat input matches the heat loss. In other words, things are still out of kilter of the TRVs are always open and the rooms never get comfortable.

What the roomstat temperature is set to is largely irrelevant, you need to set so that it's calling for heat often enough to keep the main rooms at temperature. Probably best to start it off v.high and every evening wind back one degree until the occupied rooms get nippy.

If it was mine, I'd drop a radio roomstat into the living room.

essexsi_2

Thank you all very much for your help and input.

gas4you it is a brand new Vaillant Ecotec pro 28, I will do as you say and turn the boiler stat to 70.

If I were to move the room stat to the living room, would the TRV in there have to be removed or could it just be turned to 'max'. What about the rad in the hall would a TRV need to be fitted or could it be left without?

A closer look at the room stat shows it is wireless, a BG RC plus, could I just take it off the wall and move it into the living room?

Thanks again for helping me and I'm sure all the others reading.

Cheers Si

jennifernil

DVardysShadow wrote: »

You've missed the essential knack in designing and setting up a system of this sort. The hall radiator should be slightly undersized, so that the hall does not quite reach 'stat temperature on a cold day. I had this setup in a previous house. It was always the case that if the room 'stat called OFF, it was calling ON before the rooms with TRVs had cooled noticeably.

In our system the hall radiator is deliberately undersized, so that part of the hall never gets particularly hot, so it would operate as you say. That is why I would have any "room stat" there and continue to operate our system as now.

jennifernil

stevemcol wrote: »

The idea is the room stat acts as the TRV for the last radiator in the circuit (which should have a manual valve). It prevents the boiler from firing when the overall house temperature is satisfied. If the system is designed and balanced properly the TRVs shouldn't need to demand heat when the boiler isn't fired.

I understand what you say, but I think that this could fail to respond to the many variables in a house due to its design and situation.

For example, our house is south facing and the difference in the temperature between the south facing living room and the north facing kitchen/diner can be 3 degrees when heating is not on. Added to that, our living area is upstairs, so there is no heat rising to warm the bedrooms, bathrooms and hall.

If we had a room stat in the living room,which I understand is generally the recommended place , the rest of the house would be freezing.

For us, a stat in the hall downstairs would probably be OK as it is the coldest place, but I cannot see that it would improve the system.

DVardysShadow

andrew-b wrote: »

DvardysShadow..rather than undersizing the hall rad your also missing something .... balancing the system? Backing off the lockshield valve on the hall rad and adjusting other lockshields across the house you can make it such that the other rooms all heat up quicker than the hall so they all reach the set temp on their TRVs with the stat in the hall still calling for heat. The hall rad is then constantly trying to keep up with the rads but is a "marathon runner" with the rads with TRVs on setting the pace. Even on the coldest days the hall rad then gets to full temperature and can still feasibly finish it's "marathon" attempt and relying less on heat losses from the adjacent rooms.

I see what you say, but on that system I was reluctant to manage the one radiator without a TRV using the lockshield - this rad was effectively the system bypass when all the TRV's were shut

ic

Remotely controlled radiator thermostats are available, allowing a programme to specify not only on and off times of the day for the system as a whole based on the temperature in the coldest room, but to split a system up so that one room may only be heated in the morning, and then another room in the evening. Unfortunately such systems are still expensive and the cost of setting up will likely negate any saving to be made on not unnecessarily heating rooms that don't need it. Bonus of these systems is you're not relying on a cold spot to base the controller - instead the decision to fire the boiler is based on the temperature info being returned from all the TRVs to the programmer.

See http://www.honeywelluk.com/Products/Systems/Wireless/CM-Zone/ as an example - sells on line for £550 upwards. If you're installing a new system from scratch, the hit isn't so hard, as you're going to have to spend something in the region of £180 anyway on a programmer and six TRVs anyway, but for anybody else who already has these the cost is hard to swallow.

With any luck these systems will come down in price over the next few years. Screwfix are now selling individual digital TRVs, which can independently have a programme set on them through out the day - however they still rely on the system being on at that time to provide the heat. http://www.screwfix.com/prods/71054/Plumbing/Radiator-Valves/Terrier-i-temp-i30-Programmable-Thermostatic-Radiator-Valve. I'm tempted by this solution as I'd really only need it in the main rooms I use. Every morning my living room is heated lovely and toasty - and I just walk straight through and out to work - what a waste!

slipthru

essexsi wrote: »

Thank you all very much for your help and input.

gas4you it is a brand new Vaillant Ecotec pro 28, I will do as you say and turn the boiler stat to 70.

If I were to move the room stat to the living room, would the TRV in there have to be removed or could it just be turned to 'max'. What about the rad in the hall would a TRV need to be fitted or could it be left without?

A closer look at the room stat shows it is wireless, a BG RC plus, could I just take it off the wall and move it into the living room?

Thanks again for helping me and I'm sure all the others reading.

Cheers Si

If you move the stat to the front room just turn the TRV up to max so it never switches off.

My hall rad doesn't have a TRV but as the hall never gets warm enough i'm sure it doesn't matter.

jennifernil

DVardysShadow wrote: »

I see what you say, but on that system I was reluctant to manage the one radiator without a TRV using the lockshield - this rad was effectively the system bypass when all the TRV's were shut

Same on our system.

We also do not have the free wallspace for a bigger radiator, so could not implement andrew's suggestion.