Conventional boiler problem

It is hard to argue with that conclusion :)

Thanks for that tip. There have been a few suggestions about playing with the TRV a little so I will take a look and report back (with photos).

That is the case here - the bathroom radiator is right next to the hotpress and does not have a TRV.

Are you sure it's 90 degC and not 90 degF?!

If it *is* the proper one for the job, it may just be stuck. As someone else has suggested, remove the thermostatic head from the valve and check that the pin moves down when you press on the end and comes up again when you release it. If it's stuck down it would explain your problem. Tapping the side of the valve with a metal object (spanner etc.) may free it.

Ah, that explains it. I got the impression earlier that the return pipe was cold all the way to the boiler - but now realise that it's not.

You've not mentioned a room thermostat. I assume there isn't one?

Irritatingly, the thermo does not say. I'd assumed it would be C.

Yup, I plan to do that the next time I am in the place.

That's it. The thing works very well for heating the radiators - they heat up nice and quick so the flow/return loop definitely appears to be in tip-top order. We just need to figure out what's up with the cylinder coil.

Nope, no thermostat. TBH, I've seldom if ever seen them in any houses in Northern Ireland. Oil is popular here, which is probably because there was no natural gas network up until around ten years ago, and the OFCH systems installed almost universally tend to be boilers in an outhouse with a three-port valve allowing separate control of HW and CH.

So in diagnosis, it sounds like the TRV on the cylinder is stuck closed. As otheres said you can usually unscrew the thrmostatic head using the knurled ring at its base and get a look at the valve pin. See if you can work this lose - perhaps with a bit of "shock treatment" on the valve body!

Long term you may want to "upgrade" to Y plan and add some stats. It ought to pay for itself in more efficent running if nothing else.

There is a legit use for the things to regulate the maximum temp of the HW on gravity circulated systems (i.e. older boilers with two sets of feed/return pipes and no pump involved in the HW part).

I think you may be overestimating most surveys ;-)

yup sounds that way... still at least you can see where to stick your three port valve! ;-)

But not on a system using a Primatic cylinder which is what I have and that causes the DHW to be extremely hot when the CH has been on for some time as it is just now in this weather

Stuart

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Some of the replies yesterday suggested that the thermostatic valve that we've discussed (recalling that the cylinder coil looks like just another radiator from the point of view of the system) could be jammed.

I went in for a look. The valve is a Pegler Belmont, this one :

Does this sound like it is seized up ? I guess there is about 25-30cm of

Very probably. Looking at the underside of the head, can you see what pushes on the pin? Is it small enough in diameter to go down the hole in the nut to reach the pin? If not, the pin definitely shouldn't be that low. If the actuator *does* go inside the nut, can you move the pin down more by pressing on it with a pin punch or similar? Does it come up again when you stop pushing? Can you persuade the pin to pop up by tapping the side of the valve? [Hold a large hammer against side of the valve, and tap the other side with a small hammer]

I guess there is about 25-30cm

It's probably just getting hot due to conduction in the copper pipe rather than gue to water flowing through it.

It does sound as if the pin is jammed "down" so the valve is shut and preventing the flow of water through it .....If the pin cannot be persuaded to return to the "up" position then replacement of the valve should sort the problem .

Stuart

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Try hitting it again with the head removed...

Yes...

I have not seen inside one of these particular TRVs, but on all the ones I have seen, the pin should stick up. The action of the TRV head is to progressively push down on the pin, causing the water flow to cease. A quick look at the bit you took off ought to confirm how it works. If the head looks like it has a flat surface or small recess that the pin should push against, then the pin ought to be "up" (and hence the valve "full on") when the head is removed.

Thanks for the reply. I might work up the courage to give that a shot next time I'm in the house, which should be very soon. When I did clatter it, I hit around the bottom of the valve and not the plastic head.

I looked at the inside of the head; it has a black round section with a flat surface as you have said (there is no recess though) which is spring-loaded. It definitely would not be possible for the black section to physically contact the pin at this point. I am wondering, though, how the pin managed to get below the surface of the nut with the hole, going by the way this apparently works I'd expect it to get stuck level with the nut rather than below it.

I'm a bit disturbed by the way the nut with the hole containing the pin seems to swivel around freely; I was able to twist it by hand. I am guessing this allows the valve always be open by a minimum or maximum amount at all times, with the pin then adjusting that as appropriate.

Thanks very much, Stuart. I've replied to John Rumm with more detail, but I will be mentioning the likely fault to the plumber so that he can start his investigation there.

I will need to examine it again. I take it by messing around with the valve I'm not likely to start a leak (unless I hit the pipe too hard and snap it) ?

As far as I can tell, the actuator does not go inside the nut hole, it is a flat spring loaded surface.

Will try that, thanks.

Okay.

Certainly we seem to be close to a solution here - many thanks to all who have replied. The plumber will be looking at this on Wednesday (if I can't get the pin to pop out before then) so I will pass on the details of the likely fault.

On all the TRVs I've seen, the pin is spring loaded to the up position. It should be possible to push it down by hand and it should spring up again.

You are only after shock effect here - i.e. tapping the the end of a spanner / small hammer. You are not trying to bend the pipe over! ;-)

I have been carefully reading the FAQ entry about combination boilers.

I assume I am right in believing that all of the hot water sources (bath tap, shower, and kitchen hw tap) are fed off a specific water circuit coming from the cylinder. If so, am I right in saying that provided the existing plumbing is up to scratch, installing a combi would simply be a matter of removing the existing boiler, cylinder and loft apparatus, and running a flow/return from the combi's secondary heat exchanger into the circuit formerly supplied by the cylinder, and leaving the existing CH circuit pretty much as-is ?

That way I would not have to replace the timeclock or any of the electronics, and I've only two extra pipes to install (and a few to remove) - sounds like slightly less bother (but more expense) than installing a three-port valve and controlling electronics. The diagram suggests that the three-port valve in a combi system is built into the boiler unit. It is something I think I will consider in the medium term.

I like the concept of a combi - it sounds very efficient. And, I imagine that the current boilers are also condensers so they have an extra level of efficiency that way as well.

It may be ideal for your situation considering size and type of house

However, do consider the usual warnings:

- Is the mains cold supply adequate? Measure at the cold tap in the kitchen. If less than about 20 litres/min, it may well be inadequate for a mains fed system.

- Take a careful look at HW production rate. The quoted figures of flow for a 35 degree rise in temperature approximate to what you will get in total at a shower or into a bath in the winter. Some of the smaller combis deliver 11-13 litres/min. Are you OK with that for a shower considering that stored systems can deliver 2-3 times that? Same for baths. Are you OK with 10-15 mins bath filling time?

You can get larger combis of 15-20 lpm, but they are physically large. Do you have the space? Note that the rating is not important in the CH context. If the boiler seems large, it doesn't matter because it will modulate down to the needed rate.

On the other hand, you may well find the gain in space where the cylinder and roof tanks are to be very appealing. The important thing is to do some basic checks and make sure that you select carefully.

In terms of the hookup, you have described what's involved well. It may also be necessary to upgrade the gas supply from the meter since combis normally require at least a 22mm supply pipe.

I rather fear that that would result in throwing out the baby with the bathwater!

It would be a relatively small job to add proper controls to your existing system - so why throw away a perfectly good boiler.

What you suggest would work provided you have an adequate cold water supply

You're going to be looking at a couple of grand for changing the boiler - whereas you can get a suitable control pack - which would transform your system - for as little as 60 quid. See

I have a floor standing Kingfisher ( very old one ) ,10mm piping and rads with TRV's and a Primatic cylinder a few years ago i had a BG guy out and he said that the rads and piping and TRV's wouldn't stand up to it if I got a combi boiler fitted because of the pressure .I questioned what he was saying as i couldnt see how these fittings could fail but he was insistent ...I didnt get anyhting changed and the boiler has lasted ever since altho' has probably cost me loads in gas costs .. Was he right in what he said .??

Stuart

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