Combi but no TRVs

[averagechapinthestreet]

Before anyone shouts I have searched this group and looked at the FAQ, but can=92t find anything specific enough.

Just had new combi fitted (WB 42CDi) and, despite some of the horror stories I=92ve read on here I am very impressed =96 filling the bath took a little under 8 minutes which is fine by me and I had to tighten the shower head clamp in the bathroom, such is the power of our hot water now. The installers didn=92t however put any TRVs on any of my radiators. We do have a wireless digistat panel which is in my hallway where the old analogue thermostat used to be and I can set the temp on that according to time of day, day of week etc.(as a side issue, I find this by no means intuitive and have to read the book carefully.)

My question then is do I actually need TRVs? All of the rooms in our house are used regularly (no box room etc.), but one of the reasons for changing to a combi was to save on heating fuel costs and I wonder whether the omission of TRVs may compromise that to some degree? My main concern is that my hallway is not big, and right by the front door, and though it does have a small-ish radiator there, it tends to be cold, especially if the kids are in and out a lot and (presumably) the 'ambient' temperature is measured at the digistat which could mean that the rest of the house is over-heated. Notwithstanding this, I'm happy enough to live without them, and changing now will mean a full drain-down anyway, but if there is significant enough gain to fit them, then I=92ll have it done. I would appreciate your thoughts.

Thanks everyone.

Andy.

[Slider]

Just had new combi fitted (WB 42CDi) and, despite some of the horror stories I?ve read on here I am very impressed ? filling the bath took a little under 8 minutes which is fine by me and I had to tighten the shower head clamp in the bathroom, such is the power of our hot water now. The installers didn?t however put any TRVs on any of my radiators. We do have a wireless digistat panel which is in my hallway where the old analogue thermostat used to be and I can set the temp on that according to time of day, day of week etc.(as a side issue, I find this by no means intuitive and have to read the book carefully.)

My question then is do I actually need TRVs? All of the rooms in our house are used regularly (no box room etc.), but one of the reasons for changing to a combi was to save on heating fuel costs and I wonder whether the omission of TRVs may compromise that to some degree? My main concern is that my hallway is not big, and right by the front door, and though it does have a small-ish radiator there, it tends to be cold, especially if the kids are in and out a lot and (presumably) the 'ambient' temperature is measured at the digistat which could mean that the rest of the house is over-heated. Notwithstanding this, I'm happy enough to live without them, and changing now will mean a full drain-down anyway, but if there is significant enough gain to fit them, then I?ll have it done. I would appreciate your thoughts.

Thanks everyone.

Andy.

TRV's only regulate the heat output on that radiator, they do not control the boiler. If your thermostat is in the hallway, it is the hallway temp that dictates whether the boiler fires or not. That is why the room where the thermostat is located should not have a TRV.

eg. Hallway temp 20 degC - thermo set to 25 degC Lounge temp 25 degC

if the lounge rad was fitted with a TRV it would only regulate heat from that rad. The boiler would still be firing as the hallway temp is below the desired temp.

If that makes sense!!!!

[John Rumm]

You have fitted one of the most powerful of the commonly available domestic boilers, so the hot water performance ought to be reasonable.

(Many of the horror stories result from people who fit units with a little under half the power of yours, and needless to say they will significantly less impressive when producing hot water - especially at this time of year).

Much depends on the circumstances. How evenly the house loses heat, and how well the system is balanced. If you find some rooms overheat, or for that matter you would rather have some rooms maintained at different temperature to others then you will get additional benefit from the TRVs. They will certainly save some money eventually, and will cope with the situation you describe where you end up running the heating longer than expected due to higher than usual heat loss in the hall.

[averagechapinthestreet]

I think it does! It sounds like the digistat may be in the wrong place then. I've not had a combi before and since it has only been operational for just under 48 hours I think I'll give it a bit longer to see how we go, but my first action will be to move the digistat (it's an RF one) to the lounge, and if that doesn't work think again about TRVs.

Thanks for the reply - things are a bit clearer now.

Andy.

[stuart noble]

The norm used to be to have just one TRV in the kitchen because it isn't typical i.e. you probably don't need the rad if the cooker's on.

I'd just adjust the temperature on the stat to get what you want in the rest of the house, or move the stat.

[fred]

I thought TRVs were required by Building Regs on all new systems and major works which I thought would include a boiler replacement.

You see more systems than I would in a lifetime John, what do you reckon regs wise?

My view is that however well balanced a system is designed it can get be upset by supplementary heat sources, solar gain or by cold winds outside and TRVs can compensate for that so I'd put them in.

[Roger Mills]

Ideally - possibly even legally - you should have TRVs on all but one rad, to cater for the fact that your rads are unlikely to match the room heat losses exactly (particularly in rooms where there is additional heat input from cooking, solar gain, computers, etc.) In these circumstances, TRVs save energy by turning individual rads off once their room is warm enough.

Having said that, this is not a good time of year to start mucking about with your system - wait until the summer!

Meanwhile, since you have a wireless stat, you can experiment by moving it into different rooms. You might find, for example, that it works best in the lounge and maintains most of the house at a comfortable temperature even if the hallway gets a bit cool when people keep opening the front door.

[John Rumm]

I was about to say that seemed to agree with my understanding as well, but thought it worth checking the docs. Anyway, they seem to agree:

The rules are a little different for new vs replacement systems. For a replacement you should have:

"* Boiler-based systems should have boiler control interlock in which controls are wired so that when there is no demand for either space heating or hot water, the boiler and pump are switched off

• The use of Thermostatic Radiator Valves (TRVs) alone does not provide interlock"

Heating can stay as a single zone on replacement - regardless of floor area.

Water heating:

"? All dwellings should have a separate hot water service zone in addition to space heating zones ? A separate hot water service zone is not required if the hot water is produced instantaneously, such as with a combination boiler"

Time control:

"Time control of space and water heating should be provided by: i. a full programmer with separate timing to each circuit; ii. two or more separate timers providing timing control to each circuit; or iii. programmable room thermostat(s) to the heating circuits), with separate timing of the hot water circuit. For dwellings with a total usable floor area greater than 150m2 timing of the separate space heating zones can be achieved by: i. multiple heating zone programmers; or ii. a single multi-channel programmer; or iii. programmable room thermostats; or iv. separate timers to each circuit; or v. a combination of (iii) and (iv) above Where the hot water is produced instantaneously, such as with a combination boiler, time control is only required for space heating zones"

Temperature control:

"Separate temperature control of zones within the dwelling, should be provided, using: i. room thermostats or programmable room thermostats in all zones; or ii. a room thermostat or programmable room thermostat in the main zone and individual radiator controls such as Thermostatic Radiator Valves (TRVs) on all radiators in the other zones; or iii. a combination of (i) and (ii) above"

And finally temp control of hot water:

"? Domestic hot water systems should be provided with a cylinder thermostat and a zone valve or three-port valve to control the temperature of stored hot water ? In dwellings with a total floor area greater than 150m2 it could be reasonable to provide more than one hot water circuit, each having separate timing and temperature controls. This can be achieved by: i. multiple heating zone programmers; or ii. a single multi-channel programmer; or iii. separate timers to each circuit ? The use of non-electric hot water controllers does not meet this requirement. Also, in some circumstances, such as thermal stores, a zone valve is not appropriate; a second pump could be substituted for the zone valve"

Well, I don't see that many really (not my line of work - perhaps you were thinking of John S?). But, yes, I agree, if being done by the book then one should fit TRVs.

Indeed.

[Doctor Drivel]

Just had new combi fitted (WB 42CDi) and, despite some of the horror stories I've read on here I am very impressed -

filling the bath took a little under 8 minutes which is fine by me and I had to tighten the shower head clamp in the bathroom, such is the power of our hot water now. The installers didn't however put any TRVs on any of my radiators. We do have a wireless digistat panel which is in my hallway where the old analogue thermostat used to be and I can set the temp on that according to time of day, day of week etc.(as a side issue, I find this by no means intuitive and have to read the book carefully.)

My question then is do I actually need TRVs? All of the rooms in our house are used regularly (no box room etc.),

[averagechapinthestreet]

I will read up on this (though if you could provide me with chapter and verse in the relevant legislation, that would be a great help). The installers and I did not discuss TRVs - I rather naively thought they would fit them as standard, but if they have in fact acted illegally then I will certainly call them back.

Having said that, my house is currently very toasty!

Andy.

[Doctor Drivel]

They must zone off the sleeping areas by at least temperature control (a temperature controlled zone). This can be done in a number of ways.

1) TRVs on all bedroom rads (these TRVs form a temperature zone)

2) Wall thermostat in one of the bedrooms that switches off via a zone valve all the bedrooms when setpoint is reached (most would install a stat/timer, although the time aspect is not mandatory.

[John Rumm]

Part L of the building regs defers to the Domestic Heating Compliance Guide for the detail of this. You can see that here:

> The installers and I did not discuss TRVs - I rather naively thought

They probably thought they were doing you a favour by bending the rules to save you extra expense. (although perhaps costing you more in the long term)

I can't see any explicit mention of bedrooms in the specs. They do also say that zoning on a replacement system shall be "As defined for a new system *except where boiler only is replaced*, in which case reasonable provision for a space heating system would be to control as one zone"

[my emphasis added]

[Doctor Drivel]

That is for a straight boiler swap - one in one out. "except where boiler only is replaced". A combi was fitted and the DHW altered, that is not only replacing the boiler, as other work was done - that is now as for a new system. The words "boiler only", are the key words - boiler in and boiler out, then fine, no zoning. Anything except that, then as a new system and zoning is needed.

[John Rumm]

Well the boiler was the only component "replaced" (a hot water cylinder may have been made redundant / removed - but it was not replaced), so you can still argue it either way - the document is not really that clear on this point.

(IME, very few installers zone existing heating systems on a boiler replacement - even if changing from indirect cylinder to combi)

[Ed Sirett]

The installation does not comply with current building regs. Did they sign the commissioning page? Have you received a compliance certificate?

Why should some of us go to the trouble of doing things right so others can please themselves.

I'd be very keen to know the size and layout of the gas supply pipe to the boiler. 42kW needs a big supply.

[averagechapinthestreet]

The installers didn't sign anything (that they gave to me, that is) so I haven't received a compliance certificate. The only thing I do have is the free extended warranty cert that I have to complete and send off.

In terms of the infrastructure, the boiler is in my garage and literally the other side of the wall from my meter (outside in meter cupboard), so total pipe run from meter to combi is less than 18 inches, and from memory the pipe is about an inch diameter. The installers did a cold supply pressure test with a slotted cup device held under a running tap - it was off the scale; we have very good mains pressure here.

They have additionally left the old boiler control box on the wall (the box where I set the on/off time, override etc.) still powered up so I will now have to get a spark in to isolate it and remove it. Again I didn't ask them specifically to do this, but I, perhaps wrongly, thought that they might have done it anyway. I do remember the bloke being very happy when he saw the location because he had basically no piping to do. He estimated two days to complete but in the event it took them a day plus two hours, which makes it even more difficult to understand why they didn't do the full job.

I am certain that not all plumbers are as bad, however from here onwards I will be sure to draw up a schedule of works before estimate and be less trusting in my assumptions.

Andy.

I don't want to name names on here, but I shall certainly not be recommending these people to anyone locally who asks.

[Ed Sirett]

Veyr likely dependent if push comes to shove that the install has been done properly and that includes paperwork.