Retrofit anti-cycle control?

[doppelganger]

Is it possible to retrofit an anticycle control to a system boiler?
The family like everywhere to stay warm (TRVs on all radiators) which is achievable by setting a very high temperature on the room thermostat (higher than the room TRV) - but then the boiler cycles like crazy.
The controls are Smartfit Y-plan and the boiler Worcester SB25i.
I'm imagining something that interrupts the ch demand signal from the room stat for x minutes after it last switched off, and is fitted next to (and takes its power from) the Smartfit base unit.
But does it exist?
Any thoughts or comments very welcome....

 

[JPH/01]

do you have a bypass? is the system balanced properly?.

 

[simond]

You need to take the TRV head off in the room with the Smartfit stat.

Most honeywell CM thermostat gear - but i am not familiar with Smartfit, (it is a 'I don't understand wiring' numpty system) has a software parameter where you can set the on/off delay.

 

[doppelganger]

Thanks both, impressively swift response!
Yes, there is an internal bypass - I've experimented and from full-open to closed it only changes the cycle by about 5 sec (from about 1 min). The installer fitted an external by-pass as well - might that make more difference?
I will revisit the balancing though.

Back with the "control philosophy", I started off with the TRV head off in the room with the thermostat - but the problem was that (as it says in the Honeywell user guide) " the room air temperature of the whole house is controlled from the sensor in the room unit" and when the living room has several people in it, it stays warm without heating and everywhere else then goes cold. I know I could move the stat to the hall - may or may not help much? - but it seems fundamentally better if the TRVs can be allowed to do their thing independently in each room.

(The Smartfit on-off is default set at 6 min but of course with the stat set high it never goes off)

 

[JohnD]

why not just take off the TRV head in the room with the room stat, and turn down the lockshield valve at th eother end of the rad, so that the room with the room stat heats up slower than all the other rooms? then let the wall stat turn the boiler on and off.

 

[The Baker]

I probably wont be able to solve your problem but could you tell me how long the existing boiler and controls have been installed and which make and model of boiler you have.

Thanks in advance.

Tim

 

[Agile]

I went to an old boiler today which had a retrofit anticycle device fitted to a Potty CF150.

It reminded me of your posting but as it was made in 1991 and probably no longer available I did not take any details but if you badly wanted it I could ask the client.

Its probably more helpful to reduce the power input if possible rather than adding any anticycle device.

Tony

 

[doppelganger]

Thanks again , all.
I'll try the TRV/lockshield sugestion on the living room rad.
The boiler is a Worcester 24SBi installed 2001
I will have a hunt on the web for the Potterton gadget.
I'm not sure how to reduce the power though - does that mean adjusting the burner settings or is there a control function?

 

[D_Hailsham]

Your problem is the reason all the official guides say that you should not have a TRV where the room stat is but two lockshield valves on the radiator. You also need an interlock to prevent the boiler running when it is not required.

It's all a bit idealistic; assumes all rooms heat up and loose heat at the same rate; all rooms are fitted with the correctly sized rads etc. So, when the TRV opens in one room, hey presto, the thermostat in the hall, or wherever, decides that the hall is also too cold and turns on the boiler.

You say you have TRVs on all rads and the family like warm rooms. Does that mean all TRVs are set to max? If so you might as well remove all TRV heads as they are not doing anything

There is a Smartfit parameter you can set for TRV only control. The room unit then acts only as a programmer/timer.

The info is in the installation manual, which is Here on page 5.

The problem with this solution is that the boiler will then cycle on and of according to the temperature set on the boiler thermostat; you have not provided the interlock.

 

[doppelganger]

Thanks also to D_Hailsham
This gets even more interesting....
Your comment on the offical guides and the idealistic theory articulates what I was thinking.
We're not totally profligate with heat, I guess an example of what I am trying to get round is: fair bit of background heat (bodies, TV etc) in the living room so it calls for ch only every now and then, meanwhile daughter's bedroom goes cold (she likes high temperature!).
My copy of the Smartfit manual (which was left with me in 2001) simply doesn't mention the TRV only parameter in the additional features. That is weird, 'cos mine is R(rev?)2 and the online one you linked - which must be the current version - is R1. But obviously they did contemplate TRV only control at some point. I need to see if my unit really does have parameter 04 now of course. But setting the set temp very high is going to have the same effect in practice I guess.
Meanwhile I think I have found a sensibly priced delay-off timer (Omega controls TD-73 (http://www.omega.co.uk/ppt/pptsc.asp?ref=TD-69) if all else fails.

 

[Doctor Drivel]

Meanwhile I think I have found a sensibly priced delay-off timer

For Gods sake! Just take the TRV head off the rad which the room stat is in. Sorted!!!

You NEED a control interlock that works.

 

[D_Hailsham]

[You NEED a control interlock that works.

I agree.

The problem is how do you reconcile the fact that the living room will reach the set temp quicker, due to body heat, TV, lights etc (which are not taken into account when calculating rad sizes), than the bedroom upstairs, which may not even reach the temp set on the TRV.

Taking the head of the TRV only resolves the problem of "who's in charge here?". Replacing the TRV with a lockshield valve, and adjusting this so the living room warms up slower than the bedroom, would at least ensure that the bedroom reaches temp.

(I had a very similar problem in my last house. The thermostat in the hall would shut the boiler off before any of the room rads, all with TRVs, were up to temp. The reason? The hall rad was the largest in the house and was expected to warm the hall, stairs and landing. I just closed down the manual valve on this rad a bit at a time until the stat turned off after the TRVs had kicked in.)

If I had this problem I would move the control unit out of the living room, probably into the hall as it tends to be the colder area and the traffic in and out of the house will guarantee drops in temp, so the boiler will come on. The TRV in the hall will still need to be replaced by a lockshield.

The ideal would be to install a wireless programmable thermostat and experiment with the control unit location to get the best results. But I don't know if this is possible with the Smartfit setup.

 

[Doctor Drivel]

You NEED a control interlock that works.

I agree.

The problem is how do you reconcile the fact that the living room will reach the set temp quicker, due to body heat, TV, lights etc (which are not taken into account when calculating rad sizes), than the bedroom upstairs, which may not even reach the temp set on the TRV.

Taking the head of the TRV only resolves the problem of "who's in charge here?". Replacing the TRV with a lockshield valve, and adjusting this so the living room warms up slower than the bedroom, would at least ensure that the bedroom reaches temp.

That may so it

If he wants TRVs all around on a boiler not designed for that, there is work around. The installer put a second by-pass vale. What that is supposed to achieve I don't know.

There is work around to get the control interlock. The boiler has an integral by-pass indicating that it is a system boiler with integral pump.

Get rid of the external by-pass as it is not required. Put an auto modulating Grundfos Alpha or Wilo Smart pump (£40 on s/fix) on the flow, leaving the integral pump in place. Have an external time clock and from this feed the Smart pump. After the Smart pump have a flow switch. Wire the stat circuit through this. Remove the room stat. Probably set both pumps on the lowest setting Now you have it.

The operation is: When on and all TRV open both pumps operate in series. The TRVs gradually close up, and the Smart pump slows down. When all TRVs are closed the flow switch switches out the boiler and its pumps. The Smart pumps turns very slowly and when one of the TRVs opens up enough, the flow switch detects flow and the boiler comes back in again. No flow boiler off. Flow, boiler on. If flow not great enough, the by-pass opens up protecting the boiler's heat exchanger. Simple. Costs about £70, saving the cost of room stat which knocks of £15 from that.