Heating system design query

[nemo2000]

[ Picking up from my previous thread at http://www.diy-forum.net/honeywell-st7100-help-t287143.html.......]

My heating system has a gas back boiler, gravity HW and pumped CH radiators circuit. Originally it had no cylinder or room thermostats, just TRVs on the radiators. Some years ago a 2-port zone valve was added to the HW gravity circuit, controlled by a cylinder stat, with a 2-channel programmer.

Recently the valve and/or its auxiliary switch developed an intermittent fault, leading to instances of the boiler firing while the valve was shut, so much noisy boiling and violent banging of pipework! When the boiler was serviced recently my engineer suggested there ought not to be any valve in the gravity circuit, to avoid such a problem on safety grounds.

So - should I remove the valve altogether, or would it be safe just to replace it with a new one? As I'm looking for long-term peace-of-mind to avoid potential problems, maybe the former is the better option?

 

[JohnKay]

My personal opinion would be to get rid of it. The vast majority of gravity systems never had any control of the hot water temp, and although it could be said that removal is a step back in efficiency, the boiler thermostat set to the required water temp would probably do the job in all but the coldest weather.
You'd have to waste a lot of gas to equal the cost of a replacement 28mm valve. As you indicate the peace of mind could be the deciding factor.

 

[nemo2000]

Thanks for the advice. Getting rid of an 'economy' feature does rather go against the grain in these costs-concious days, but I would rather not renew the valve and then be wondering what on earth might be happening every time I was away from the house!

Now to TRVs please......originally there were no TRVs, but I fitted Drayton TRV2s many years ago in every room *except* the bathroom and on the landing. The landing radiator is rather small and struggles to keep the area warm, so it seemed pointless to fit a TRV that probably would be set on MAX all the time. I can't recall now why the bathroom was not done at that time.

The bathroom radiator was physically rather too big for the room and used to get very hot, to the extent of a slight risk of scalding if you happened to brush against it for too long. When the bathroom was refurbished it was replaced by a smaller one, but with convector fins, sized (as best I could) to supply the necessary BTUs. At the same time a TRV was fitted so that the temperature could be regulated. In practice it has run for some years with the TRV head removed (!) and seems to be 'about right'.

As several of the TRVs are becoming unreliable with age, and other work is planned which needs the system to be drained anyway, I'm going to have all the TRVs replaced by new ones (probably Drayton TRV4). On the assumption that at least one radiator should not have a TRV, should I keep put one on the bathroom, or one on the landing, or neither? Any factors to consider which I may have overlooked please?

 

[JohnKay]

The TRV4 is a good valve, I've used them for years. and should be a straight swap.
Some older gravity systems were piped up with the bathroom rad, or towel rail on the hot water circuit to provide heat in the summer. If that is the case, leave the TRV off the landing.
If all the rads are on the pumped circuit, the choice is yours. The idea of having one radiator without a TRV is only to ensure a minimum flow rate.