Heating controls question

[Robert Irons]

Hi all

I might be needing to get some new central heating controls set up in the near future. Is this a job for any electrician or do some plumbers do this sort of thing themselves?

 

[cross thread]

Most heating installer’s fit them and so do electricians so ask the ones you use

 

[BlueLoo]

Do you mean the fitting or the specification or both?

I wouldn't trust either to do both in isolation.

Do your own research.

 

[ericmark]

A heating and ventilation engineer should be able to do all involved with heating and ventilation. Plumber is a worker of lead, clue in the name, and would be trained how to wipe pipes or roofs I suppose even organ pipes, all of which are historic, so in real terms the trade no longer exists, so hard to say what some one labelled as a Plumber is trained to do.

Pipe fitter is a completely different trade, I have worked with them fitting thick wall 32" pipes and I simply would not know where to start, a very skilled trade.

But even electrician is such a wide trade, I as an electrician have programmed PLC's (programmable logic control) and worked on some very complex systems, but I remember the first time I worked on my daughters central heating (Y Plan) and I was struggling to work out how to test it, OK I know now, but having the label electrician or plumber even if we did have same Union does not mean we know central heating, however neither does it mean we don't.

I have a problem with my own central heating, I am sure in fullness of time I will sort it, but although I understand the wiring if one can't see the pipes, then there is a little guess work involved.

Also gas and oil are different, and solid fuel is very different, with solid fuel there is a delay between stopping the supply of fuel and the heat stopping, with oil there is only an on/off, where with gas the water heater (normally called a boiler even when if it boiled one would call it a fault) can modulate, that means it has a variable output.

So for the moment I will assume gas, with a modulating boiler, some can be directly interfaced with the likes of OpenTherm so the control system tells the boiler what output is required, others the boiler is actually controlled by the return water temperature.

So we can install systems like EvoHome or Wiser where we have basic a hub collecting information from a series of TRV heads and the hub tells the boiler what to do. The problem is price, and some one who is trained can work out how to use cheaper options, could use for example terrier i30 or the eQ-3 TRV heads in most rooms, these are stand alone programmable TRV heads, and only use the expensive type in one or two rooms.

It is a balance between price and functionality, there is no right or wrong, the boiler needs to be allowed to modulate to work in an efficient way, so working well and working efficient are not the same, but there are many ways to achieve the same result.

With oil in some ways easier, as simple on/off, however there are other problems, trying to stop a hysteresis is complex, and there is a balance again, also in the main central heating also heats domestic hot water, in my case there is no electrical link between the DHW store and the boiler, some times there is a tank thermostat, and some times a motorised valve, but not in my case.

So I would say a heating and ventilation engineer can do the job, but that does not mean a plumber or electrician can't do the job. I had a central heating expert look at my system and he admitted he did not understand the modern electronic controls I had fitted, so the labels on the trade do not help.

 

[Robert Irons]

Crikey @ericmark that was a bit more than I was expecting and shows theres clealy a bit more to it than I had realised.

But since youve so kindly educated me perhaps you could enlighten me on a few things!

My system is currently a Worcester Bosch 15ri heat only boiler, with the bog standard Honeywell dual channel wired programmer (https://www.screwfix.com/p/honeywell-home-st699-programmer/86588). It is a Y plan system and all the controls and pump are on the first floor. I have a TADO smart thermostat hard wired in to the system.

1) My 'boiler' is causing me grief at the moment- it will only heat the feed pipe to a maximum of about 55-57 degrees. The return pipe is usually around 15 degrees lower. The boiler is only 4 years old. After draining system, re-filling, cleaning, getting rid of some air-locks and even replacing pump, I have come to the conclusion that the boiler needs servicing and possibly there is something wrong with the heat exchanger. It takes quite a long time for the water in the feed to reach 55 degrees even with the boiler on max. From what you've written above it sounds like some heating controls will actually ask the boiler for a certain level of output? On my TADO app this is suggested but had assume this was just a question of telling the boiler to cycle (ie just come on for x% of time) rather than varying its output per se. I had thought my old Honeywell programmer would have been a simple on/off job and not capable to of sending the boiler a command to 'send heat at 70% output' for example.

2) I want to put wet underfloor heating downstairs, where the boiler is. Are there any control systems you are aware of that can send a command to a 2 way valve wirelessly - ie basically I want to leave the cylinder upstairs where it is but pump will move downstairs and ideally would like something that can tell the valves on 1st floor to open for rads/ hot water ,but which doesnt require new wiring run between the cylinder and the location of the boiler. I haven't managed to find anything which looks like it would do this.....

Thanks

 

[ericmark]

Job one is look what boiler should do.

You will notice there is a range, so looking at 18 kW 5.54 kW to 18.48 kW and when in mothers house which also had a modulating boiler I found it hard to tell if the boiler was ticking over or running flat out, here with an oil boiler easy it only has one output, so if running that is output, but the return water temperature can control the boiler output.

As far as I am aware only Bosch thermostats can connect to the ebus, so tado can only switch on/off. However some thermostats use a mark/space ratio to stop over shooting it reduces the hysteresis, good idea with oil, but with modulating gas it defeats all the cleaver algorithms built into the boiler, temperature control needs to be done with the TRV head, not wall thermostat, all the wall thermostat is for is to switch off the boiler on a warm day.

I found with mothers house setting the lock shield valve was the main thing to get boiler to work well, not being a heating engineer I do not have a differential thermometer to set the temperature drop across each radiator, so I used the turn off until pipes cold, then turn on until feel the slightest bit of heat, working out from boiler, it improved things, but not good enough.

So I used the TRV the computer shows both target and current, so if current exceeds target then close the lock shield a small amount, and after trimming the lock shields the TRV's kept the room within 0.5°C of set point and worked very well, except when other heat sources caused problems like sun in bay window.

Once set I found the radiators ran a lot cooler, as the boiler was modulating so getting a constant heat just enough to maintain the room temperature not the all or nothing I was getting before they were set. Since the radiators ran cooler, when the sun hit the bay windows they stopped heating room faster so less over shoot caused when sun came out.

My intention was fit electronic TRV heads and then a wall thermostat to control them, however they worked that well never bothered with new wall thermostat.

I did however find the built in anti hysteresis was OTT, so set the TRV at 22°C at 7 am then 20°C at 8 am to speed up reheating after being on over night, this meant the geofencing was useless, would never hit heat on time, so used simple time control.

I read the Drayton Wiser TRV head has algorithms built in to work out how long it takes to heat the room, so can reheat rooms faster without over shooting, but never tried them.

As to UFH had electric version in the wet room, totally useless, it just took too long to heat up the room, maximum floor temperature set at 27°C and that is simply too cool to heat the room, needs radiators as well.

Using geofencing the idea is speed, so iVector fan assisted radiators to reheat fast, but UFH is slower than standard radiators will not work with geofencing. The iVector is so expensive so I would use a plinth fan assisted in the kitchen, but standard radiators in other rooms, the plinth fan assisted does warm the floor so no need for UFH in kitchen.

But remember I am an electricians not a plumber or heating engineer.