Radiator valves (TSR's)

[Dean]

Hi,

After much deliberation I've decided on a glow-worm 38CXi combi boiler to replace the vented system we already have. However at the moment we control the temperature in each room with TSR's (I think thats what they are known as) on each radiator, which we turn up or down as required.

I like this system and don't want to have a wall-mounted thermostat "feeding back" the temperature in one room to the 38CXi. They are ugly and poor at regulating a whole house temperature (the north facing living room needs more heating than our south facing bedroom).

My question is will using TSR's on the radiators, with a 38CXi combi cause any problems that I should be aware of?

Thanks for any help received,

Dean.

[Grunff]

TRVs? (thermostatic radiator valve)

[IMM]

They are referred to as: TRVs. 38CXi? Good choice. The 38CXi is fitted as standard: a inbuilt bypass, filling loop, 2-stage frost protection and anti-seizure controls.

The by-pass ensures that if all TRVs are closed the boiler will have enough flow through the heat exchanger.

The regs say a control "interlock" must be provided. This is to cut out the boiler when there is no heat demand and prevent cycling. A wall stat may be fitted in the hall and use this as a high limit. If the TRV is set to give say 21C set it to 25C. The boiler will cycle though, but only on the lowest gas rate as the burner will modulate to the lowest setting.

There are other ways of achieving an interlock with a wall stat, but it involves flow switches and Grundfoss Alpha pumps.

[Tony Bryer]

A big plus for the CXi is that it will modulate down to a low level when demand is low (6.6kW for the 38CXi). However if you just have TRV's when they all shut down the boiler will just keep cycling which is seriously wasteful. If you really don't want a room stat then there are flow switch options but I have no experience of them.

I spent the weekend completing my 24 CXi swap over - the hw cylinder came out and its feed now handles the bedroom area as a separate zone now with 2 CM67's running independent programmes. If splitting your property into two zones was practicable, this would be the best solution IMHO.

[IMM]

How does this go? is it quiet? performance? etc?

[Tony Bryer]

All seems pretty good so far - you know when it's running but nothing unacceptable. One of the key reasons for choosing the Glow-worm 24Cxi was that it modulates down to 4.9kW and with split zones in a relatively small place the heating load on each zone is not very different to this. It's in what is now an open plan living room/kitchen so not only was I concerned about noise per se, but also wanted to reduce the tendency for it to shut on and off (which can be more annoying than a steady background noise). With only 24kW bath filling is abysmal - I can't remember when I last soaked in a bath - but shower is transformed as compared with the 1.5m head Mira 8 (which was fine if you didn't know anything else). The 30Cxi would have cost £100 more and needed the gas supply to be rerun in 28mm. The next owner may curse my choice but it's fine for me.

On the more general point, where you get homes constructed to the latest BRegs standards (or better) with very low CH loads for a lot of the year, coupled with a desire for bigger combis for better DHW performance, ISTM that the challenge for combi makers will be to see how little heating they can deliver rather than how much.

[IMM]

A friend has recently bought a big flat. One bathroom and one bathroom en-suite. It was served by a Vaillant giving 11-12 litres min. Sounds vastly under specced for the demand. But the slow bath fills she is already used too from the old flat, and its no bother. She turns on the bath and then gets ready while it fills. But she takes showers most of the time. It will do two showers reasonably well, but the prospect of two baths at once is a no, no. An event she does not see happening. The combi is about a year old, so she is keeping it. A higher flowrate model could fit in the cupboard, but still two baths at once is a tall order. At the other end of the flat, at the end of the hallways a cupboard could be built in wasted space to house another combi, and have the water system, CH, split. At least the option is there.

That is exactly how they are viewing it. DHW demand will increase, and in most newer homes after the next insulation hype, DHW demand will exceed CH. Also instant DHW will be more in demand as people's lifestyles change.

[John]

One interesting point I have come across recently is the use of a rotary flow detector on the tapwater in the Cxi range. We have pretty hard water up in our area and I've had two new boilers which suffered flow detector failure while within guarantee. No particles visible in the strainers or in the detector or other visible causes of jamming so called Glow Worm who came out and replaced the detector units. I'd be interested if this was just bad luck or if theres a pattern emerging here

[IMM]

Or probably someone who did not put a de-scaler on in a hard water area. Some W-B models have turbione flow detectors. They will give the flow rate, not just an on-off signal.