Almost there with the piping

The renovation of my sons flat is well underway. As regards central heating I followed the advice on here and have gone the manifold route. Due to there being only four radiators I have been able to connect from manifold to radiators in Speedfit with no intermediate joints.

Just a couple of questions I would be grateful for your help please.

It is an indirect system with hot water cylinder in the airing cupboard. I propose to join the hot water return below the return from radiators manifold ie on the boiler side. Will I need to put a check/non return valve between the manifold and the T joint fitting where the hot water return enters to stop backflow and make sure the hot water return goes only to the boiler along the resulting one pipe.

My own house has the bathroom and ensuite towel radiators fed from the cylinder hot water flow and exiting to the hot water return. This works well as in the summer with no central heating on but hot water heating still active, the towel warmers still operate.

As the flat set up has two small created from one bathroom can I do the same as they are both within 1.5 metres of the airing cupboard.

With these two queries sorted everything will be ready when the Gas engineer comes to fit the boiler in the New Year.

You would normally have a 3 port valve to direct the water between the rads, and the hot water tank; this allows the tank and the rads to heat in the winter, and just the tank to heat in the summer. You don't need a check valve to stop the water going back into the system, but as long as it fits into the return pipe after the rads, the the pump flow should be positive from the boiler, and negative on the return side.

Grateful for the quick response, initially it was my intention not to put in the non return valve, but a comment by a builder in the local pub started me thinking that perhaps in the summer convection from returning hot water would find the way back to radiators - you have put my mind at rest.

Any ideas about my second question, can I tap into the flow and return of the hot water heating pipes to heat bathroom towel rails independent from central heating. They would be very small towel rails around 700 btu's each.

If you want the towel rad on in the autumn and spring, then you'd tap it into the hot water tank circuit, and then turn the rad off in the summer - which is what I think you're after. If you only have the towel rad on when the other radiators are on, then tap it into the nearest rad pipe work.

If this is a new heating installation, it will have to comply with Part L of the building regulations which require the use of a motorised valve (or valves) in conjunction with a room thermostat and cylinder thermostat to provide a 'boiler interlock'. Any Gas Safe engineer who you ask to install the boiler will not do so, without these being in place.

Once the boiler interlock is in place, if you were to connect the towel warmer to the hot water circuit, because the hot water cylinder thermostat will stop the cylinder heating up once it is hot, the towel warmer will also go off. Usually the cylinder will only take about 20 to 30 minutes to reheat, and this may only happen twice a day depending on your hot water usage, so the towel warmer will be off for most of the time.

It's a good thing to point out Stem, but the towel rad going off when the hot water is fulfilled, is a normal scenario. The assumption being that you want the rad to be working at the same time as the tanks being heated as well. But you either have the towel rad on all year round for a short period, or only on when the rads are in use, but for a longer period. I wonder if Dolph has considered fitting the towel rad to the radiator circuit, but getting one that has an electric heating element in it for the rest of the year.

The boiler installer may well be happy to fit the thermostat after the boilers in, and I've never had one insist they are in place first, but it's possible that I've always found the easy going ones. So Dolph, what have you considered in terms of the stat etc, and has anyone overseen this project - or is it all your own work. Are you insulating all the pipework, and being plastic, is it well supported, because I was horrified the first time I saw a plastic pipe get hot.

None of the Gas Safe guys I know would ever commission a new system not fitted with a boiler interlock. When you say "I've always found the easy going ones" are you really saying that you are aware of Gas Safe engineers willing to flout the building regulations ?

depending where the pipes run, it's possible to tap into the flow and return prior to the 3-port valve, or whatever. I've done that for my bathroom rad. But you have to wind the lockshield right down, or it will act as a bypass and steal flow from the rest of your system. And fit a TRV of course.

dolph said:

Will I need to put a check/non return valve between the manifold and the T joint fitting where the hot water return enters

Click to expand...

Actually, it's not just unnecessary, but actually you'd need a second expansion vessel in the loop. This is because when the boiler goes off and the water starts to contact, the water in the isolated loop will drop below atmospheric pressure and if the nrv is good, air will be pulled in through any tiny leaks. If all the joints really are good, the water will be in a vacuum and therefore expand to fill the space. With a second expansion vessel it would take up the slack.
But all completely unnecessary as said before.

Or do the job properly and have the bathrooms on a separate zone.

Thank you all so much for taking the time to consider my "project". No NRV required saves me effort. As regards hot water flow and return to Towel Warmers my own in my own home, which was built in the 70's, have supplied two towel warmers and one larger bathroom rad. The system is connected to the two pipes that go in and out of the hot water cylinder coil, never had any problem. The water is timed to heat 3 times a day and the towels seem to dry OK, hence my question with my two boys' flat, their warmers would be 700x400 601 BTU's. As I was thinking of using 10mm pipe, thought the offtake would be minimal off 22mm pipes.

Perhaps I should explain. I am not doing anything with the boiler. The Gas Safe man told me, probably like you guys, he is very busy at the moment and the routing of piping, especially as we want it buried/hidden was not something he really wanted to do at present and we would have to wait until May probably. As I have been a competent DIYer for 40 years+, helped on many occasions by this site, your dads probably, he suggested I do the piping bringing it to within a metre of the boiler. So off to Screwfix bought a Titan wall chaser (amazing tool I have found) and I have constructed channels, fed the protected plastic piping through these from the manifold and achieved a joint free system except at manifold and rads, both easily accessible. Also as he requested taken a wire from HW cylinder to boiler space and also the same for room thermostat - this will cover Boiler Lock.

The electrician saw my chasing. so now I have got the job doing channels for him and making holes for his sockets, saved me money and done a job that neither man would rather not do, certainly getting my worth out of the Titan! Basically I am just doing the donkey work.

Thanks again, you do a great service on here, I for one really have appreciated it over the years, learned so much.

dolph said:

The water is timed to heat 3 times a day and the towels seem to dry OK, hence my question with my two boys' flat, their warmers would be 700x400 601 BTU's. As I was thinking of using 10mm pipe, thought the offtake would be minimal off 22mm pipes.

Click to expand...

Don't forget though that when the system has the required 'boiler interlock' that the hot water will only be heated for occasional short periods of time. They won't work like yours do. So would be better connected to the heating circuit. I know of several that didn't work satisfactorily after a new boiler was fitted had and had to be connected to the heating circuit.

My suggestion would be if you want the best of both words plumb the towel warmer in as a bypass before the zone valves. Then if the boiler is on then the towel rail is on, but you're not wasting anything by running it when the HW is up to temperature.
You can additionally put a proper radiator in or plinth heater, connected to the normal heating circuit, if you have a high heat loss in winter.

As said above is a good option and complies with part L building regs. Having the towel rad on only when hot water is being heated could result in it only being heated for very short periods as newer cylinders take far less time to heat up and their heat losses much less.

As I should have expected, following discussions with my sons yesterday, before the haze of wine, beer etc. took over, they confirmed your consensus view to be correct. It would be much preferable for the towel warmers to be connected to central heating as in the summer the flat gets so hot that anything dries in there naturally!! I think I will however leave a spare piece of unconnected wire in the stud wall just in case an electric rad heater element is needed, costs nothing but could save so much time just in case.

Anyway thanks to all of you that replied, as always very grateful for your input. Can I just wish you all a very happy and prosperous New Year.