Central heating system with no thermostat (again)

[Robin]

An idiot boy question please I've not found answered in the Wiki or previous posts: is there any easy way I can check if a gas CH/hot water boiler really *needs* at least one radiator without a TRV?

Background

Elderly relative has a bungalow with gas boiler (not combi) for unpressurised CH and hot water via tank. It was built with TRVs on all radiators and without a thermostat. She used it like that for 16 years w/o problems. On my infrequent visits I didn't notice a lot of cycling but that could be down to my lack of attention/nous.

I've just found out a BG "engineer" she called under her service plan to fix stuck TRVs last year told her she *must* have one radiatior without a TRV on - the one in the hall. She leaves the doors from the hall to kitchen, bathroom and bedroom open during the day so she has since been heating most of the place other than the living room she spends most time in, at much greater cost than before.

To make matters worse I don't know the make/model of the boiler or programmer; and would only be able to make a flying visit over the holiday period. So I hope at least to be able to do enough to tell her, as a temporary measure at least, to use all the TRVs again until I or another fits a stat. (I think I u/s the Wiki's point about energy wasted by the boiler cycling when all rooms are up to temperature. But ISTM even more is wasted by it trying to heat the hall etc without limit).

[The Natural Philosopher]

fit a radio stat in the hall?

[John Rumm]

There are two reasons for having a non TRV rad; one is when it is in the same room as the main room stat. If it has its own TRV, then it could possibly shut off the heat before the main stat is satisfied, and leave the heating always "on". The second is to prevent a situation where there is no flow path though the whole system.

The second case can be sidestepped with an automatic bypass valve. Some boilers include these anyway.

So the "need" for the stat in the first case is for fuel and energy saving[1], and in the second its to keep the system working without either prematurely wearing out the pump or causing the boiler to lockout due to an overheat trip.

Since the system worked well for years before, it would suggest that there was some alternate path for water through the system. This might be an automatic valve in the boiler (check make and model), a separate one plumbed into the system, or even just a manual bypass such as a gate valve turned mostly off, or a rad in the bathroom that is always on etc.

From where you are now, it might make sense to leave it as it is, but fit a wireless room stat.

[1] Needless to say that only works when you actually have a room stat - it sounds rather like the fitter was following "the rules" without understanding why they were not appropriate in this case.

[Robin]

Thanks but I don't have the confidence to fit a stat during a flying visit over the holidays when the price of failure would be so high (ie no heating/hot water and a king's ransom to get professional support).

And while I would like to fit a stat (in the living room where she spend most time) is wireless really the best thing for an elderly person who is not that good with LCDs even after her cataract operations? I'd thought in terms of a wall mounted dial with clear black-on-white numbers.

[Tim Lamb]

In message , Robin writes

My Potterton boiler of that vintage has the model legend on the front.

You might be able to do a remote control identity check:-)

We have bathroom radiators with no TRVs and a conventional roomstat in the hall. Not ideal but I do try to ensure the hall TRVs are set high and working. The boiler still cycles on its overtemp thermostat when the heating system is returning hot water but with the hall stat still calling for heat.

More modern boilers have the ability to modulate the output but you need someone with more knowledge to explain that:-)

[Martin Brown]

Perverse lateral thinking solution to this problem would be to insulate the hall radiator with a blanket or the foil backed polystyrene sheet. And/or get her to close more of the doors in the hallway.

(this wouldn't work for my parents as my mum is convinced that anything left on a hot water radiator overnight could catch fire)

Why didn't the BG muppet install the non-TRV radiator valve in the smallest room in the house (usually the bathroom or kitchen towel rail)?

It is a nightmare fighting with an unknown legacy heating system with no documentation or circuit diagrams - even more so on a flying visit.

[Andrew Gabriel]

We can't answer this without knowing the make/model of the boiler.

Old boilers which heat an internal tank of water don't need a bypass. If the hot water cylinder is gravity fed, this is almost certainly what you have. You might still have a problem if the plumbing layout is such that if all the TRV's closed, you end up pumping over in the small header tank in the loft and heating that up.

Not quite such old boilers with low water content need an external bypass loop of minimum length or a radiator which is always on, to absorb the heat which is put into the heat exchanger in the delay between it reaching the boiler temperature and the control ciruits detecting this and switching off the burners.

Some newer low water content boilers have the bypass loop built in, and don't need an external one.

If you want to reduce the output from that radiator without any plumbing changes, you can cover it partially or completely with a towel or something similar, to thermally insulate it.

[John Rumm]

or tweak down the lockshield when visiting...

[Dave Liquorice]

Agreed. The system has worked fine for 16 years in full TRV mode and no room stat, there can't be all that much wrong with it.

Did the fitter check:

That the boiler actually needs a bypass? With no stat one assumes that the pump runs all the time that the CH is on via the programmer and the boiler cycles on it's stat. Not ideal from an energy consumption point of view but it was how things were done, it's not allowed now.

For the precense of an automatic bypass valve or manual bypass (gate valve cracked open)?

Before pronuncing that "... she *must* have one radiatior without a TRV on - the one in the hall." I doubt it, they were just spouting the rules that apply to new systems and even then badly as adding a room stat would stop the boiler cycling when the house is warm. From what you say it seems that this British Gas person has just made your relative use more gas for no real reason. Who do they buy thier gas from, not British Gas is it? ...

[The Other Mike]

Bugger the clear digits and analogue dials, fit one where the elderly operator can't fiddle with it and they remain warm.

[DerbyBorn]

The Other Mike wrote in news: [e-mail]:

+1 With a programmed thermostat there is no need to fiddle with it.

However, on most it is realitivly easy to train someone to use the up or down button which will change the existing time period.

[ARW]

Piece of piss to fit and if you want I'll have my phone on for free technical installation advice (if you want).

[Robin]

Many thanks for all the information/suggestions/offers of help from you and others. I'll try to digest further in time to take enough kit to do more than curse BG and tweak* down the lockshield. But I may end up sitting in the loft, watching the header tank, and sending futher plaintive requests for guidance.

*I have clearly been reading material of the kind which ought not to pollute my tired old eyes as I initially misread your post as "twerk down the lockshield". I am sure you are flexible enough to do so but I'd be buggered if I tried it :)

[MJA]

One thought -- there are some boilers, such as the Baxi Solo, that can use a flow sensor as an interlock to shut off the boiler when all the TRVs are satisfied.

We don't know what boiler the OP's relative has, but it may be worth checking as fitting a bypass could cause the symptoms observed.

Such an installation meets the requirement for a boiler interlock without a room thermostat.

MJA

[bert]

In message , Robin writes

Take the TRV off in the living room and put it on in the hall - and tell her to shut the f+++++++ doors,

[bert]

In message , Robin writes

You would be if you twerked whist sitting on it.

[fred]

In article , bert writes

Leaving the lounge without any means of temperature control other than the boiler stat, hardly the most consistent and comfort oriented method of control.

Good advice given already.

Also bear in mind that a radiator with the TRV set to max is just as effective as an uncontrolled dump radiator in the short term.

[Roger Mills]

Depends what you mean by short term - an hour or two maybe?

It will still close when the room temp is high enough, even on max.

[fred]

Not in my experience, TRV max is in the range 23-25degC so if the room temp can reach that in normal operation then the boiler stat needs turning down.

Once the boiler stat is within reasonable limits then maxing a TRV is equiv to an open rad. Not perfect equiv but as close as makes no diff in practical terms.

Short term can then be as long as it takes for the o/p to install a proper system control.

[John Rumm]

I find it hard enough getting down to a lockshield - one of the disadvantages of being a TFB is low and small places and spaced pose interesting challenges ;-)