Are Bulldog TRV heads interchangeable?

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I'm having problems with one radiator in the house (colder than it should be) and think the problem lies with the 11 year-old Bulldog TRV. From its age, I assume it's a Gen 1 valve. It's the only Bulldog in the house, so I can't just swap the head with another Bulldog to check. I'm happy to buy a complete valve and just use the new head, but the only Bulldogs for sale are Gen 2 and someone has told me that the Gen 1 and Gen 2 heads aren't interchangeable. Can anyone confirm whether this is correct or not? Otherwise I'll have to change the whole valve, which will be a hassle.
 
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I did previously remove it - and it did cure the problem. At least it got the previously cold rad up to a bit above lukewarm - so now I'm thinking the system needs balancing. But I still need a new head for the faulty valve (or a whole new valve :( )
 

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I think they'd be interchangeable, a lot of different manufacturers are, so Bulldog to Bulldog imo should fit. If it became warm at the top, and hot at the bottom it’ll just need bleeding.
 
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Thanks Chris, I think you're right. I'll give Peglers a ring and see if they can confirm. I wish it was just bleeding needed, but the rad just became warm all over. A few other rads are also playing silly buggers, which is why I think balancing must be the answer.
 
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Most of the TRV heads are M30 x 1.5 mm, some early ones seem to be larger I know I had a problem in old house, there is also the Danfoss RA, RAV and RAVL which need adaptors that came with my replacement head. It also seems the amount the pin moves varies as well, so if it is M30 x 1.5 mm the easiest way is to get a head which auto adjusts to the pin. The eqiva eQ-3 programmable TRV head for example, if not within limits it shows F2 actuating range too wide, or F3 actuating range too small.

When I got 5 bluetooth eQ-3 heads they cost me £15 each, seems price went up when we left the EU, the non bluetooth were £10 each, there is also the terrier i30 however not used them so don't know if they tell you when out of range, the Energenie did not, and in spite of costing a lot more, did not allow manual setting, and did not include so many options as to how to fit on the TRV base, it does state a range up to 25 mm, and comes with a 28 mm and 30 mm fitting, and two spacers to adjust range 2 mm and 3.5 mm, but I would say all in all the eQ-3 are better in spite of not connecting to internet.

I got the Energenie first, which do show on the PC both current and target, did not work so well with an on/off oil boiler I have now, but with the modulating gas boiler I used the current and target reading to set the lock shield valve. 4 TRVs-1.jpg the method was if the current exceeded target to close lock shield a small amount. One set to be fair they were within 0.5°C of setting when used with a modulating boiler, and I moved them around radiator to radiator to set the lock shield valves, once all set those with old wax heads were also spot on, found TRV's work better on supply side, on the return there is more of a tendency to over shoot.

The eQ-3 only shows target temperature, so can't be used to set in same way.

Son had a boiler fitted and all lock shields left wide open, and it worked A1 until turned off at Christmas when he went to visit in-laws and turned it off, on switching on again it heated radiators one at a time, but as long as there is no wall thermostat turning off whole system it does start working again, however it would not work for me as I turn heating off over night.

As each TRV closes it pushes water to next, however since the boiler modulates it turns the boiler output down prematurely, so with a modulating boiler having lock shield set correct is important for a fast warm up, my oil boiler is quite small so I set the times on the TRV's so rooms are heated in sequence to speed up the reheat after being turned off.

At £10 for programmable head it did not seem to make sense to use non programmable.
 
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Thanks very much ericmark, that's definitely given me a lot to think about. Programmable certainly seems the way to go - or at least give one a try!!
 
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