Room stat needed for combi?

[Sean]

We have a WB 24 CDI combi that doesn't have an externally mounted room stat fitted, although one can be connected.

All of the radiators have stats on - am I right to assume that the boiler has an internal stat that senses the (heating) water temperature as it flows though the system and adjusts dependant on how high up front panel knob is turned? - Or does the water just get heated to a higher temperature irrespective of the heat lost via the radiators?

I'm wondering if there are any advantages to having a room stat for this boiler.

Thanks.

[John Stumbles]

Probably not: my guess is the lazy and/or ignorant installer skimped on it. What does it say in your Benchmark log book under Time/temperature control fitted?

Energy efficiency, compliance with regs and longer life of the boiler.

[Sean]

errrmmm .... there is just a set of instructions, no log book.

So am i right to think that there is a stat in the boiler that is the only temp control for the CH system?

[Christian McArdle]

There is a legal requirement to have one fitted for energy efficiency reasons (at least for new installations and replacement boilers), unless an alternative form of "boiler interlock" is provided. However, any installer specifying a 24kW combi sounds like the sort of cheapskate that wouldn't even know what a boiler interlock was.

Without one, your boiler will be churning away wasting energy even when your house is hot.

Christian.

[Ed Sirett]

The log book if found will be either a couple of pages in the instruction manual or a Bluish A4 card folded in A5. Alas, not having the look book is the going rate.

The only other control will be the valves on the individual radiators. The boiler will have an adjustable setting for the radiator temp, that's all you have. If this system was installed after 1/4/5 if was not done legally. If before it was simply defective.

[Sean]

Can you explain what you mean by your phrase

"However, any installer specifying a 24kW combi sounds like the sort of cheapskate that wouldn't even know what a boiler interlock was. "

Arent you making an assumption on the size of the house the boiler is fitted to?

There is obvioulsy some form of stat in the boiler itself as it does turn on/off and does seem to maintain a level temp.

[Christian McArdle]

Nope. It is a combi, which is sized for water demand, not the size of the house. 24kW is only just OK for a shower.

Given the marginal price difference between a 24kW and a 28kW, it seems pointless saving yourself two pounds fifty and losing the extra power, which makes all the difference in such a marginal installation.

Christian.

[Dave Plowman (News)]

It's too small to supply a decent flow of hot water.

[Sean]

Now i'm wondering who i can believe on here - the boiler has been running for 4+ years in a large 3 bed house with 8 rads connected and other than the usual moans about having to wait 10 minutes to fill a bath no one has moaned about the lack of heat output from it.

My initial question has only been promted by the fact that the recent tennants have left giving me the opportunity to carry out some work - including (if needed) a remote room stat.

If i undertsand the responses so far i'm looking at having to replace the boiler - or have i missed the point?

[Christian McArdle]

There's no need to replace the boiler. The type of boiler was just mentioned in that it supports the idea of a penny pinching attitude by the installer. Adding a room stat to the existing setup is a very good idea. The best room for it is the lounge, provided it doesn't have a separate heater, like a gas fire. In the room with the stat, you must remove any TRVs on the rads and replace them with lockshield valves that the tenants can't turn off. Ensure all the other rooms do have TRVs on them.

Christian.

[Dave Plowman (News)]

The heat output is more than adequate for the CH - just not for the hot water as you've discovered.

[Ed Sirett]

Whilst I agree the difference between the 24kW and 28kW boilers is only marginal. (Maybe the gas pipework was not good enough to support

28kW?)

If the original installer truly penny pinching then he would have installed a HeatLine/Biasi/Ravenheat/Wickes/Halstead or similar. The difference to a B-W would have been several hundred quid. Although not fitting a room thermostat was a truly dire ommission.