Upgrading the Central Heating System- BOOM!

[Alan Dempster]

Folks,

Seeing as this is the right time of year to attempt DIY on our Central Heating without freezing to death, I thought I'd delve into a little project to upgrade our system.

The house that we bought towards the end of last year has a CH system that could only be described as 'crude' at best! The boiler is in the garage, and sports a gravity hot water system, with pumped central heating. There was (until recently), a naff old Randall 102 timeswitch, which totally failed to either keep good time (typically losing up to 1 hour per day) or to switch on/off at the defined times.

So, phase 1 of my upgrade project was to replace the CH programmer. I chose an ACL Drayton unit, a Tempus 7. Good programmer, looks much better, and with jumpers set correctly, behaves as I would expect - i.e. allowing HW control on its own, or CH AND HW together (turning on HW pulls up the CH also).

But here's the weird thing: our CH cylinder also has a tank 'stat, but there are NO motorised zone valves anywhere in the system. Now this, to me, is rather odd. I also stripped and rewired the 'wiring centre' at the same time; as all the power to the boiler in the garage was old and flaky, I have installed a double socket, a fused spur (with appropriately rated 3A fuse) and a 'wiring centre' which in this case, is a blanking plate over a ton of cabling in a flush-mount box, suitably earthed!)

As far as I can tell, the mains from the fused spur feeds the timer. The 'HW On' signal from the timer goes via the Cylinder stat and fires the boiler if the Cylinder stat says 'Go!'

The 'CH On' signal from the timer goes via a Room stat in the living room, and fires the water pump, if the room stat says 'Go!'.

To cap it all, there's a Honeywell Frost stat in the garage, which connects the boiler directly to the mains, if the temperature drops to

+5 deg C. In this circumstance, this ensures that the boiler always fires, if the Frost stat says 'Go!'....

So my questions are as follows:

1. The Drayton Tempus 7 seems like a good choice of programmer. But there's also a similar model, a Lifestyle LP722, which seems similar BUT it does have a fancy-looking backlit display, which might look funky in the dark! Are there any differences between these two 7-day programmers? Recommendations?

1. I'd like to replace the crusty old Honeywell room 'stat in the lounge with a new Programmable Thermostat. But is there any point now that I've installed the Tempus 7 programmer?

2. Should I install a pipe-stat as well as the Honeywell frost stat in the garage, to protect the boiler? Or would this be unneccesary with a properly installed Room stat in the living room (probably still required for boiler protection, I guess).

1. How the hell does my HW system manage to regulate its temperature without any zone valves? The Honeywell Cylinder stat certainly seems to be doing something....

2. Can I bang a 2-port motorised valve into this system to upgrade it to a C-plan? I understand that there are venting safety issues with doing this.. FWIW, the Water Pump is sited directly beneath the boiler in the garage.

The whole thing really does seem like an odd bodge, although I'm guessing that I could upgrade it to a properly split CH/HW system, with a bit of extra effort.

All advice would be welcomed, particuarly around the Programmer / Digital Room stat issue.

Cheers all,

Big Al.

[Christian McArdle]

Any programmer would do. To be frank, most modern systems could work with a couple of switches. A modern lagged cylinder can be heated 24 hours day. A programmable thermostat will handle timing for the heating zones. I fitted a programmer to mine, but only ever select "Off" or "24H". I have a cylinder stat, heating the cylinder 24/7 and 3 (shortly to be 4) separate heating zones with their own programmable thermostats.

Yes. Programmable thermostats have advantages that can't be replicated by a standalone programmer. The advantages include convenient access (i.e. living room), ability to set a nighttime temperature (i.e. 10C, rather than -273C) and anticipation of switch on time (i.e. coming on early if it is particularly cold).

You might as well. However, it is particularly important to lag the CH pipes to the garage. Better still, replace any metal with plastic, as it is less prone to freeze damage.

Well, it is a simple upgrade. It isn't foolproof, but is a massive improvement on a system without the stat.

Basically, with the CH On and the room thermostat activated, the hot water will get heated anyway (and might get too hot). However, in the summer, with the CH Off, the boiler will only fire when the hot water cylinder is cold. This will MASSIVELY improve fuel efficiency and maintain the hot water at the selected temp. Fitting the extra zone valve (or pump) will improve efficiency further and prevent overheating of the water when the central heating is on. It would improve efficiency still further to pump the circuit, if possible.

Yes you may normally. However, this may be dependent on the boiler. Some boilers require an open gravity loop for heat dissipation, which precludes using a valve. This isn't very common in gas fired boilers, though.

All open vented boilers require an open unvalved path from the boiler to the vent. Most will also require an open unvalved path from the cistern outlet to the boiler not shared with the vent path. What options are available to you depend on your boiler and its safety features.

Christian.

[Set Square]

Sorry, I've only used Honeywell.

It depends on whether the Tempus 7 provides independent *timing* control over HW and CH - and whether you want this. Many programmers only essentially have one clock. If you have a programmable room stat, you can set the Tempus 7 to provide "continuous" CH - and can actually control when the CH comes on and off with your room stat. This can be at different times from when the HW is on, and you can have different temperatures at different times of the day. A programmable room stat also acts as a frost stat in its "off" position.

With the boiler being in the garage, this could possibly freeze up before the frost stat in the house turns the system on. Maybe *just* a pipe stat - wired to bring the boiler on when the pipe falls below (say) 5 degC - is all you need to protect the boiler itself. Your programmable room stat will protect the rest of the house.

In a half-hearted way? Someone appears to have attempted to provide a boiler interlock, but has only done half a job! In HW-only mode, the boiler will turn off when the HW gets up to temperature. However, in CH mode, the HW will get hotter than the cyl stat setting whenever the boiler is on.

Presumably you have a vented system, with vent and fill pipes connected into the HW circuit near to the cylinder? You should be ok if you can insert a

2-port zone valve in the the HW flow pipe very close to the cylinder, *after* the vent pipe connection - thus continuing to provide an unrestricted path from the boiler to the vent.

You might be able to convert it to an S-Plan system if you can pump both circuits and insert another zone valve in the CH circuit. Are there currently 4 boiler connections - with separate circuits for HW (gravity) and CH (pumped)? If so, you'll either need another pump (and the control logic then gets a bit complex!) or you'll need to reduce the boiler connections to

3 - by tee-ing the CH flow pipe into the HW pipe a little way from the boiler rather than leaving it directly connected. You can then put your (single) pump in this common bit of pipe before the tee. You can keep the separate return connections.

With 2 zones valves cutting off *all* flow, you *might* need a by-pass circuit - but that is unlikely with a boiler which can survive with a gravity system.

HTH.

[Tony Bryer]

I put a Lifestyle in for my mum last month, and it seems fine - three on/off times each day, (except on the cheapest model) run heating and hw programs independently of each other.

For myself I've got 2xHoneywell CM67's controlling my heating (2 zones)

- far more flexible if you take time to learn what the different buttons do. You can do things like having a overnight setback temperature for cold nights or kill the heating for five hours if you're going out.