Want to replace Drayton Digistat but don't know what to buy

[pippin]

We have a Worcester Bosch 28 cdi boiler. The thermostat, a wireless Drayton Digistat SCR, is playing up and seems to have a mind of its own.

We've got the impression that there are problems with wireless thermostats, so we're considering replacing it with a wired one. But we don't know what to get.

We don't need to programme it to come on at certain times or on certain days or anything like that... we just need to be able to set the temperature we want the heating to be on at.

Any suggestions would be gratefully received.

 

[croydoncorgi]

There are 3 models of radio Digistat: RF!, RF2 and RF3.
It sounds like you've got the RF3 that some people consider to be about as user-friendly as a cornered rat.

A new RF1 will do exactly what you say you want and it and the new SCR will fit straight onto the existing backplates, so no wiring to do.

But before you waste your money: what EXACTLY is wrong with the existing box? and which model is it? In my experience, almost all the problems are at the other end of the finger!

 

[pippin]

We have a Digistat RF1. It was installed two and a half years ago with the new boiler. We noticed that the red light on the receiver would stay on as a solid light for minutes at a time. It would flash, then the boiler would fire up, and then a minute later the boiler would go off and the solid red light would be back on again. We thought it might be the batteries, so we replaced them, but that didn't work.

The Worcester Bosch service engineer gave the boiler itself a clean bill of health. He said it's the Digistat that's the problem.

Anyway, at the moment the receiver seems to be getting a signal on and off, and has a mind of its own. It can work for hours and then start playing up again.

We were considering getting another wireless one, but we're worried that we'll have the same problem.

 

[EliteHeat]

Do you particularly need an RF stat?

 

[croydoncorgi]

Before you lash out the cash, do this first (if only to humour me - although I get heartily sick of Digistats which are 'dead on arrival', when they work they're usually OK, in my experience).

Turn the CH system OFF at the main switch, so there's no power to the SCR box.

Take all the batteries out of the RF1.

Turn the power back on. The red light on the SCR should go on.

Push and HOLD IN the buttons on the SCR IN THE ORDER 1 followed by 2, until the red light goes off.

Put the batteries back into the holders on the RF1 and CLOSE THE RIGHT HAND HOLDER BEFORE THE LEFT ONE.

After a short delay, the red light on the SCR should start flashing at about 2 flashes / sec. This is the 'handshake' between RF1 and SCR, making the SCR remember the unique ID of the RF1, to distinguish it from all other RF1s and other kit using the same radio system.

If you now press the plus button to increase the setpoint, the SET message should flash on the RF1 display and a little flame image should appear to the left of the temperature display. Very soon after that, the red light on the SCR should flash some more and then the green call-for-heat light should come on too, and the boiler should fire.

End of RF1 lesson Don't even think of asking how to program an RF3.

It is COMPLETELY NORMAL for the red light on the SCR to flash about every 10 minutes - the RF1 updates it with Call or Not Call regularly. but unless the little flame image is showing on the RF1 display, the heating won't come on!

The temperature normally showing on the RF1 display is the ACTUAL temperature, NOT the setpoint.

HINT It's much easier to do all this if you take the RF1 off the wall (loosen one grub-screw) and take it near to the SCR, so you can see both at once!

 

[ChrisR]

Beat me to it. I've also found they usually ARE ok. And you can't rely on the "low battery" signal, because the radio bit packs up before the thermostat/display bit every time, and the dud battery symbol is for the ones which last longer

 

[pippin]

Ok, did that...

Everything seemed fine... flashing in all the right places, heat came on... five minutes later back to the solid red light and no heating. The flame is on the thermostat, but the receiver still has the solid red light and the boiler doesn't fire. Eventually, after about a minute, the solid red light changes to a flashing one again, and the heating comes on, but then off it goes a minute later (while the little flame is still on the thermostat) and we're back to the solid red light.

I can hear it coming on and going off... it seems to be a law unto itself.

 

[ChrisR]

Ok, yours is broke.

Usually they're pretty reliable. Before you buy a plain one, look at what something like a Honeywell CM67RF can do for you. Doddle to use and everyone I've put them in for loves them.

 

[ollski]

It's usually the receiver unit that faults up at about 50.00 a shot.

 

[pippin]

Ok, I'll have a look at the Honeywell... I like the "doddle to use" part.

Just in case we don't go for the Honeywell, are there any we should avoid?

Oh, and can we do the wiring ourselves, or will we need an electrician?

We have to get it replaced pretty quickly... after a whole day of living in a fridge, we woke up last night in a sauna. Apparently, no matter how hot or cold it is in here, the thermostat thinks it's 26 degrees.

 

[croydoncorgi]

On the principle that lightning never strikes the same place twice, get the same RF1 / SCR again - then there's absolutely NO wiring to do.

Dunno what backplate and wiring layouts the Honeywell box uses - just possibly the same. ChrisR might know.

 

[BlueNasser]

Croydon, just wanted to say thanks. Followed your advice to the letter about changing the batteries in my RF2 unit. Heating is now working as required. Thanks.

 

[bengasman]

I have had the same problem with several digistats. Replaced them with Honeywell cm 927 and they all still work. These are also more userfriendly.

 

[ChrisR]

The battery contacts on digistats are poor. You can completely remove the 1 or 2 "drawers" which hold them, and poke a rubber or similar up inside to clean those.
I think I've got 3 sets of "dead" digistats which had nothing else wrong with them.
And don't rely on the "dead battery" symbol. The RF side goes flat first but the symbol reads the non-RF side's batteries

ALso, they'e too expensive. Tower do one much cheaper, which is pretty good.
Honeywell would still be my 1st choice though. There are others - siemens, sunvic...