Fitting TRV - further question

[Mr E]

I've got 13 rads and will be fitting TRV's to 11 of them. The rad in the hall (where the room stat is located), and the bathroom rad will be excluded. Do you think I should still fit a differential pressure valve, or will the 2 excluded rads be enough of a pressure release? Bearing in mind its a small bore 10mm system with conventional header tank.

Thanks again.

Mr E

P.S. Pegler Terrier TRV's from Screwfix arrived and look very nice! Thanks for all the previous suggestions.

[Andy Hall]

I think it should be, but it will depend on how the balancing works out. In other words, if the pipework length is short and results in a good flow to these radiators vs. others then you may have to turn down the flow a lot to get others balanced in. THis might then result in too low a flow for bypass purposes, but I rather doubt that this would happen.

Realistically, you can only try it out and see. I would do the radiator valves and refill, test and balance. Then go and turn off the 11 TRVs and check that the bypass is still enough that the boiler overrun is working OK and that there is not any sign of boiling.

Then if you do need to add an automatic bypass you can, and finally add inhibitor.....

.andy

To email, substitute .nospam with .gl

[Dave Gibson]

Fit a Grunfoss Alpha Pump and it will optimize the system flow.

Dave

[Mr E]

Thanks. I will try out first as you suggest, and if needed will consider fittting a new Grundfoss Alpha pump as per Dave Gibson's post. Easier work and only a bit more expensive to have the clever pump to control the pressure!

Mr E

[Mr E]

I wasn't aware of this 'new technology' (?). Having read up a bit I can see it would be an ideal solution. I'm going to see how things run without, and if needed will fit this pump (about 55 quid), instead of plumbing in a bypass valve. Thnaks.

[Andy Hall]

These are good pumps and do what they say - I have one for my workshop circuit.

However, dropping the pump power level because of the incrreased flow resistance is only part of the story, useful though it is. The boiler, unless it is a modulating type, will require a minimum flow rate immediately after the flames go off and until the heat exchanger cools. It is really that which the bypass addresses.

As I mentioned, with what you are proposing, I reckon that it will probably be OK, but if the boiler has a tendency to boil, then dropping the flow rate won't address the issue - you would need to get more water through it in that case - hence the bypass.

.andy

To email, substitute .nospam with .gl

[Mr E]

[Mr E]

Take care,

John.

[MIKE THORNE]

I would stick with Andy's first post, the 10mm pipe run to the hall rad could well be enough on it's own but if you've got the towel rail in the bathroom as well, which unless you live in a bungalow will probably be fed in 15mm you should be fine.

[Mr E]

Thanks, I'm going to do just that and see how it works out, with 2 of the rads excluded. (No towel rail, there is just a rad in the bathroom also fed with 10mm). I'll follow Andy's advice as you suggest, and feel pretty sure I won't need any further work to do. I will make sure though and test things out before putting the inhibiter in!

Appreciate all the advice.

[BillV]

The two combi boilers I've fitted in the couple of years both had auto-bypass valves built in... I guess this is because the manufacturers assume that they will be used on all TRV systems.